Optical element, light guide element, and image display device

ABSTRACT

Provided are an optical element that can make the brightness of light emitted from a light guide plate uniform, a light guide element, and an image display device. The optical element includes a patterned cholesteric liquid crystal layer that is obtained by immobilizing a cholesteric liquid crystalline phase, in which the patterned cholesteric liquid crystal layer has a liquid crystal alignment pattern in which a direction of an optical axis derived from a liquid crystal compound changes while continuously rotating in at least one in-plane direction, and the patterned cholesteric liquid crystal layer has regions having different pitches of helical structures in a plane.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. Application No. 17/034,535,filed Sep. 28, 2020, which is a Continuation of PCT InternationalApplication No. PCT/JP2019/014241, filed on Mar. 29, 2019, which claimspriority under 35 U.S.C. § 119(a) to Japanese Patent Application No.2018-064084, filed on Mar. 29, 2018, and Japanese Patent Application No.2018-231784, filed on Dec. 11, 2018. Each of the above applications ishereby expressly incorporated by reference, in its entirety, into thepresent application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to an optical element that diffractsincident light, and a light guide element and an image display deviceincluding the optical element.

2. Description of the Related Art

Recently, as described in Bernard C. Kress et al., Towards the UltimateMixed Reality Experience: HoloLens Display Architecture Choices, SID2017 DIGEST, pp.127-131, augmented reality (AR) glasses that display avirtual image and various information or the like to be superimposed ona scene that is actually being seen have been put into practice. The ARglasses are also called, for example, smart glasses or a head-mounteddisplay (HMD).

As described in Bernard C. Kress et al., Towards the Ultimate MixedReality Experience: HoloLens Display Architecture Choices, SID 2017DIGEST, pp.127-131, in AR glasses, for example, an image displayed by adisplay (optical engine) is incident into one end of a light guideplate, propagates in the light guide plate, and is emitted from anotherend of the light guide plate such that the virtual image is displayed tobe superimposed on a scene that is actually being seen by a user.

In AR glasses, light (projection light) projected from a display isdiffracted (refracted) using a diffraction element to be incident intoone end portion of a light guide plate. As a result, light is introducedinto the light guide plate with an angle and propagates up to anotherend portion in the light guide plate while being reflected from aninterface (surface) of the light guide plate. The light propagated inthe light guide plate is also diffracted by the diffraction element inthe other end portion of the light guide plate and is emitted from thelight guide plate to an observation position by the user.

As this diffraction grating, a diffraction element formed of liquidcrystal is known.

For example, JP2017-522601A describes an optical element comprising aplurality of stacked birefringent sublayers configured to alter adirection of propagation of light passing therethrough according to aBragg condition, in which the stacked birefringent sublayersrespectively comprise local optical axes that vary along respectiveinterfaces between adjacent ones of the stacked birefringent sublayersto define respective grating periods. The optical element described inJP2017-522601A diffracts transmitted light. JP2017-522601A describesthat light incident into a substrate (light guide plate) is diffractedby an optical element such that the light is incident at angle at whichthe light is totally reflected in the substrate and is guided in adirection substantially perpendicular to the incidence direction of thelight in the substrate (refer to FIG. 7 of JP2017-522601A).

JP5276847B describes a polarization diffraction grating comprising: apolarization sensitive photo-alignment layer; and at least first andsecond liquid crystal compositions that include a polymerizable mesogenand are arranged on the photo-alignment layer, in which an anisotropicalignment pattern corresponding to a polarization hologram is arrangedin the photo-alignment layer, the first liquid crystal composition isarranged on and aligned by the alignment layer and at least partlypolymerized, the second liquid crystal composition is arranged on andaligned by the first liquid crystal composition, and both the liquidcrystal compositions have a thickness d of a layer determined by theformula d ≤ dmax = Λ/2, where d represents the thickness of the layerand A represents a pitch of the polarization diffraction grating.

WO2016/194961A discloses a reflective structure comprising: a pluralityof helical structures each extending in a predetermined direction; afirst incidence surface that intersects the predetermined direction andinto which light is incident; and a reflecting surface that intersectsthe predetermined direction and reflects the light incident from thefirst incidence surface, in which the first incidence surface includesone of end portions in each of the plurality of helical structures, eachof the plurality of helical structures includes a plurality ofstructural units that lies in the predetermined direction, each of theplurality of structural units includes a plurality of elements that arehelically turned and laminated, each of the plurality of structuralunits includes a first end portion and a second end portion, the secondend portion of one structural unit among structural units adjacent toeach other in the predetermined direction forms the first end portion ofthe other structural unit, alignment directions of the elementspositioned in the plurality of first end portions included in theplurality of helical structures are aligned, the reflecting surfaceincludes at least one first end portion included in each of theplurality of helical structures, and the reflecting surface is notparallel to the first incidence surface.

Here, in AR glasses, in a case where light propagated in a light guideplate is diffracted by a diffraction element after adjusting thediffraction efficiency of the diffraction element, it is known that aviewing zone expands (exit pupil expansion) with a configuration inwhich a part of light is diffracted at a plurality of positions to beemitted to the outside of the light guide plate.

For example, WO2017/180403A describes an optical waveguide including aninput-coupler (diffraction element), in which the input-coupler coupleslight corresponding to an image and having a corresponding field of view(FOV) into the optical waveguide, splits the FOV of the image coupledinto the optical waveguide into first and second portions, and diffractsa portion of the light corresponding to the image in a second directiontoward a second-intermediate component, and an intermediate coupler(diffraction element) and an output-coupler (diffraction element)performs exit pupil expansion.

However, a screen using a cholesteric liquid crystal layer that isobtained by immobilizing a cholesteric liquid crystalline phase isknown.

The cholesteric liquid crystal layer has wavelength selectivity inreflection and reflects only circularly polarized light in a specificturning direction. That is, for example, the cholesteric liquid crystallayer reflects only right circularly polarized light of red light andallows transmission of the other light.

By using the cholesteric liquid crystal layer, for example, atransparent projection screen through which an opposite side can be seencan be realized.

Light reflection by the cholesteric liquid crystal layer is specularreflection. For example, light incident into a cholesteric liquidcrystal layer from a normal direction (front side) is reflected in thenormal direction of the cholesteric liquid crystal layer.

Therefore, the application range of the cholesteric liquid crystal layeris limited.

On the other hand, WO2016/194961A describes a reflective structureincluding a cholesteric liquid crystal layer, in which light can bereflected with an angle in a predetermined direction with respect tospecular reflection instead of specular reflection.

This reflective structure includes a plurality of helical structureseach of which extends in a predetermined direction. In addition, thisreflective structure includes: a first incidence surface that intersectsthe predetermined direction and into which light is incident; and areflecting surface that intersects the predetermined direction andreflects the light incident from the first incidence surface, in whichthe first incidence surface includes one of two end portions in each ofthe plurality of helical structures. In addition, each of the pluralityof helical structures includes a plurality of structural units that liesin the predetermined direction, and each of the plurality of structuralunits includes a plurality of elements that are helically turned andlaminated. In addition, each of the plurality of structural unitsincludes a first end portion and a second end portion, the second endportion of one structural unit among structural units adjacent to eachother in the predetermined direction forms the first end portion of theother structural unit, and alignment directions of the elementspositioned in the plurality of first end portions included in theplurality of helical structures are aligned. Further, the reflectingsurface includes at least one first end portion included in each of theplurality of helical structures and is not parallel to the firstincidence surface.

SUMMARY OF THE INVENTION

In a case where a liquid crystal diffraction element is used as adiffraction element of a light guide element used in AR glasses anddiffracts a part of light at a plurality of positions to be emitted tothe outside of the light guide plate for viewing zone expansion (exitpupil expansion) ofAR glasses, there is a problem in that the brightness(light amount) of light emitted from the light guide plate isnon-uniform in a case where the diffraction efficiency in a plane of theliquid crystal diffraction element is uniform.

An object of a first aspect of the present invention is to solve theabove-described problems of the related art and to provide an opticalelement that can make the brightness of light emitted from a light guideplate uniform, a light guide element, and an image display device.

The reflective structure (cholesteric liquid crystal layer) described inWO2016/194961A includes the reflecting surface that is not parallel tothe first incidence surface.

Therefore, the reflective structure described in WO2016/194961A reflectsincident light with an angle in the predetermined direction with respectto specular reflection instead of specular reflection. For example, inthe cholesteric liquid crystal layer described in WO2016/194961A, lightincident from the normal direction is reflected with an angle withrespect to the normal direction instead of being reflected in the normaldirection.

As a result, in WO2016/194961A, the application range of the reflectivestructure including the cholesteric liquid crystal layer can beextended.

However, in the reflection of light from the cholesteric liquid crystallayer, a so-called blue shift (short-wavelength shift) in which thewavelength of light to be selectively reflected shifts to a shortwavelength side occurs depending on angles of incidence light.

Therefore, the cholesteric liquid crystal layer described inWO2016/194961A reflects light with an angle in the predetermineddirection with respect to specular reflection, and thus has a problem inthat the amount of reflected light decreases due to influence of blueshift (short-wavelength shift) as the reflection angle increases.

In particular, in the case of a reflection element having a lensfunction, the reflection angle varies depending on incidence positionsof light as described in WO2016/194961A. Therefore, there is adifference in the amount of light reflected depending on incidencepositions in a plane of the element. That is, there is a region wherethe brightness of light reflected is low depending on incidencepositions in a plane of the element.

An object of a second aspect of the present invention is to solve theproblem in the related art and to provide an optical element thatreflects light using a cholesteric liquid crystal layer, in whichincident light can be reflected with an angle in a predetermineddirection with respect to specular reflection and the amount of lightreflected is also large.

In order to achieve the object, the first aspect of the presentinvention has the following configurations.

An optical element comprising a patterned cholesteric liquid crystallayer that is obtained by immobilizing a cholesteric liquid crystallinephase,

-   in which the patterned cholesteric liquid crystal layer has a liquid    crystal alignment pattern in which a direction of an optical axis    derived from a liquid crystal compound changes while continuously    rotating in at least one in-plane direction, and-   the patterned cholesteric liquid crystal layer has regions having    different pitches of helical structures in a plane.

The optical element according to [1],

in which in the patterned cholesteric liquid crystal layer, a pitch of ahelical structure increases from one side toward another side in thein-plane direction.

The optical element according to [1] or [2], comprising:

-   a plurality of cholesteric liquid crystal layers,-   in which the cholesteric liquid crystal layers have different    twisted directions of helical structures, and-   at least one of the cholesteric liquid crystal layers is the    patterned cholesteric liquid crystal layer.

The optical element according to [3], comprising:

-   the patterned cholesteric liquid crystal layers having different    twisted directions of helical structures,-   in which in the patterned cholesteric liquid crystal layers having    different twisted directions of helical structures, directions in    which the direction of the optical axis derived from the liquid    crystal compound continuously rotates in the liquid crystal    alignment pattern are different from each other.

The optical element according to [3] or [4],

in which the cholesteric liquid crystal layers having different twisteddirections of helical structures have the same selective reflectioncenter wavelength.

The optical element according to any one of [1] to [5], comprising:

-   a plurality of patterned cholesteric liquid crystal layers,-   in which the patterned cholesteric liquid crystal layers have the    same twisted direction in helical structures.

The optical element according to [6], comprising:

-   the patterned cholesteric liquid crystal layers having the same    twisted direction in helical structures,-   in which in the patterned cholesteric liquid crystal layers having    the same twisted direction in helical structures, directions in    which the direction of the optical axis derived from the liquid    crystal compound continuously rotates in the liquid crystal    alignment pattern are the same as each other.

The optical element according to [6] or [7],

in which the patterned cholesteric liquid crystal layers having the sametwisted direction of helical structures have different slope pitches.

The optical element according to any one of [1] to [8],

in which in a case where a length over which the direction of theoptical axis derived from the liquid crystal compound rotates by 180° ina plane is set as a single period, the length of the single period is 50µm or less.

The optical element according to [9],

in which the length of the single period is 1 µm or less.

A light guide element comprising:

-   a light guide plate; and-   the optical element according to any one of [1] to [10] that is    disposed on a surface of the light guide plate,-   in which the optical element is disposed such that a helical pitch    of a helical structure of the patterned cholesteric liquid crystal    layer gradually changes toward a traveling direction of light in the    light guide plate.

A light guide element comprising:

-   a light guide plate;-   a first diffraction element that is disposed on a surface of the    light guide plate and diffracts light to be incident into the light    guide plate;-   a third diffraction element that diffracts light propagated in the    light guide plate to be emitted to an outside of the light guide    plate; and-   a second diffraction element that diffracts light propagated from a    position of the first diffraction element in the light guide plate    in a direction toward the third diffraction element,-   in which at least one of the second diffraction element or the third    diffraction element is the optical element according to any one of    [1] to [10].

The light guide element according to [12],

in which each of the second diffraction element and the thirddiffraction element is the optical element according to any one of [1]to [10].

The light guide element according to [12] or [13],

-   in which each of the first diffraction element, the second    diffraction element, and the third diffraction element is a    cholesteric liquid crystal layer that has a liquid crystal alignment    pattern in which a direction of an optical axis derived from a    liquid crystal compound changes while continuously rotating in at    least one in-plane direction, and-   in a case where lengths of single periods of the liquid crystal    alignment patterns in the first diffraction element, the second    diffraction element, and the third diffraction element are    represented by Λ₁, Λ₂, and Λ₃, respectively, Λ₂< Λ₁, and Λ₂< Λ₃ are    satisfied.

An image display device comprising:

-   the light guide element according to any one of [11] to [14]; and-   a display element that emits an image to the light guide element.

The image display device according to [15]

in which the display element emits circularly polarized light.

In order to achieve the object, the second aspect of the presentinvention has the following configurations.

An optical element comprising:

-   a patterned cholesteric liquid crystal layer that is obtained by    immobilizing a cholesteric liquid crystalline phase,-   in which the patterned cholesteric liquid crystal layer has a liquid    crystal alignment pattern in which a direction of an optical axis    derived from a liquid crystal compound changes while continuously    rotating in at least one in-plane direction,-   the patterned cholesteric liquid crystal layer has regions having    different pitches of helical structures in a plane, and-   in a case where a length over which the direction of the optical    axis derived from the liquid crystal compound rotates by 180° in a    plane is set as a single period, the patterned cholesteric liquid    crystal layer has regions having different lengths of the single    periods.

The optical element according to [17],

-   in which a plurality of regions having different lengths of the    single periods in the liquid crystal alignment pattern are arranged    in order of the length of the single period in the patterned    cholesteric liquid crystal layer,-   the plurality of regions having different pitches of helical    structures are arranged in order of the length of the pitch of the    helical structure, and-   a direction of a permutation of the lengths of the single periods is    different from a direction of a permutation of the lengths of the    pitches of the helical structures.

The optical element according to [17] or [18],

in which in the patterned cholesteric liquid crystal layer, the lengthof the single period in the liquid crystal alignment pattern graduallydecreases from one side toward another side in the in-plane direction inwhich the direction of the optical axis derived from the liquid crystalcompound changes while continuously rotating in the liquid crystalalignment pattern.

The optical element according to any one of [17] to [19],

in which the liquid crystal alignment pattern is a concentric circularpattern having a concentric circular shape where the in-plane directionin which the direction of the optical axis derived from the liquidcrystal compound changes while continuously rotating moves from aninside toward an outside.

The optical element according to any one of [17] to [20], comprising:

-   a plurality of cholesteric liquid crystal layers,-   in which the cholesteric liquid crystal layers have different    twisted directions of helical structures, and-   at least one of the cholesteric liquid crystal layers is the    patterned cholesteric liquid crystal layer.

The optical element according to [21] comprising:

-   the patterned cholesteric liquid crystal layers having different    twisted directions of helical structures,-   in which in the patterned cholesteric liquid crystal layers having    different twisted directions of helical structures, directions in    which the direction of the optical axis derived from the liquid    crystal compound continuously rotates in the liquid crystal    alignment pattern are different from each other.

The optical element according to [21] or [22],

in which the cholesteric liquid crystal layers having different twisteddirections of helical structures have the same selective reflectioncenter wavelength.

The optical element according to any one of [17] to [23], comprising:

-   a plurality of patterned cholesteric liquid crystal layers,-   in which the patterned cholesteric liquid crystal layers have the    same twisted direction in helical structures.

The optical element according to [24], comprising:

-   the patterned cholesteric liquid crystal layers having the same    twisted direction in helical structures,-   in which in the patterned cholesteric liquid crystal layers having    the same twisted direction in helical structures, directions in    which the direction of the optical axis derived from the liquid    crystal compound continuously rotates in the liquid crystal    alignment pattern are the same as each other.

The optical element according to [24] or [25],

in which the cholesteric liquid crystal layers having the same twisteddirection of helical structures have different slope pitches.

The optical element according to any one of [17] to [26],

in which the length of the single period in the liquid crystal alignmentpattern is 50 µm or less.

In the first aspect of the present invention, it is possible to providean optical element that can make the brightness of light emitted from alight guide plate uniform, a light guide element, and an image displaydevice.

In the second aspect of the present invention, it is possible to providean optical element that reflects light using a cholesteric liquidcrystal layer, in which incident light can be reflected with an angle ina predetermined direction with respect to specular reflection and theamount of light reflected is also large.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual diagram showing an example of an optical elementaccording to a first aspect of the present invention.

FIG. 2 is a plan view showing a cholesteric liquid crystal layer of theoptical element shown in FIG. 1 .

FIG. 3 is a conceptual diagram showing an action of the cholestericliquid crystal layer of the optical element shown in FIG. 1 .

FIG. 4 is a conceptual diagram showing one example of an exposure devicethat exposes an alignment film of the optical element shown in FIG. 1 .

FIG. 5 is a schematic graph showing a relationship between a positionand a diffraction efficiency.

FIG. 6 is a diagram schematically showing an example of an image displaydevice including the optical element according to the first aspect ofthe present invention.

FIG. 7 is a graph schematically showing a relationship between aposition and the intensity of emitted light.

FIG. 8 is a front view schematically showing another example of a lightguide element including the optical element according to the firstaspect of the present invention.

FIG. 9 is a top view of FIG. 8 .

FIG. 10 is a diagram showing a method of measuring an emitted lightintensity in Examples.

FIG. 11 is a schematic diagram showing a method of measuring thediffraction efficiency.

FIG. 12 is a conceptual diagram showing an example of an optical elementaccording to a second aspect of the present invention.

FIG. 13 is a conceptual diagram showing a patterned cholesteric liquidcrystal layer of the optical element shown in FIG. 12 .

FIG. 14 is a plan view showing the patterned cholesteric liquid crystallayer of the optical element shown in FIG. 12 .

FIG. 15 is a conceptual diagram showing an action of the patternedcholesteric liquid crystal layer of the optical element shown in FIG. 12.

FIG. 16 is a conceptual diagram showing one example of an exposuredevice that exposes an alignment film of the optical element shown inFIG. 12 .

FIG. 17 is a conceptual diagram showing an action of the optical elementshown in FIG. 12 .

FIG. 18 is a graph showing an optical element according to a secondaspect of the present invention.

FIG. 19 is a plan view showing another example of a patternedcholesteric liquid crystal layer of the optical element according to thesecond aspect of the present invention.

FIG. 20 is a conceptual diagram showing another example of an exposuredevice that exposes the alignment film of the optical element shown inFIG. 19 .

FIG. 21 is a conceptual diagram showing a method of measuring a lightintensity.

FIG. 22 is a diagram conceptually showing another example of the opticalelement according to the second aspect of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an optical element according to a first aspect of thepresent invention, a light guide element, and an image display devicewill be described in detail based on a preferable embodiment shown inthe accompanying drawings.

In the present specification, numerical ranges represented by “to”include numerical values before and after “to” as lower limit values andupper limit values.

In the present specification, “(meth)acrylate” represents “either orboth of acrylate and methacrylate”.

In the present specification, the meaning of “the same” includes a casewhere an error range is generally allowable in the technical field. Inaddition, in the present specification, the meaning of “all”, “entire”,or “entire surface” includes not only 100% but also a case where anerror range is generally allowable in the technical field, for example,99% or more, 95% or more, or 90% or more. In addition, “perpendicular”or “parallel” regarding an angle represents a range of the exact angle ±5°, and “the same” regarding an angle represents that a difference fromthe exact angle is less than 5 degrees unless specified otherwise. Thedifference from the exact angle is preferably less than 4 degrees andmore preferably less than 3 degrees.

In the present specification, visible light refers to light which can beobserved by human eyes among electromagnetic waves and refers to lightin a wavelength range of 380 to 780 nm. Invisible light refers to lightin a wavelength range of shorter than 380 nm or longer than 780 nm.

In addition, although not limited thereto, in visible light, light in awavelength range of 420 to 490 nm refers to blue light, light in awavelength range of 495 to 570 nm refers to green light, and light in awavelength range of 620 to 750 nm refers to red light.

In the present specification, a selective reflection center wavelengthrefers to an average value of two wavelengths at which, in a case wherea minimum value of a transmittance of a target object (member) isrepresented by Tmin (%), a half value transmittance: T½ (%) representedby the following expression is exhibited.

-   Expression for obtaining Half Value Transmittance: T½ = 100 - (100 -    Tmin) ÷ 2

In addition, selective reflection center wavelengths of a plurality oflayers being “equal” does not represent that the selective reflectioncenter wavelengths are exactly equal, and error is allowed in a rangewhere there are no optical effects. Specifically, selective reflectioncenter wavelengths of a plurality of objects being “equal” represents adifference between the selective reflection center wavelengths of therespective objects is 20 nm or less, and this difference is preferably15 nm or less and more preferably 10 nm or less.

In the present specification, Re(λ) represents an in-plane retardationat a wavelength λ. Unless specified otherwise, the wavelength λ refersto 550 nm.

In the present specification, Re(λ) is a value measured at thewavelength λ using AxoScan (manufactured by Axometrics, Inc.). Byinputting an average refractive index ((nx+ny+nz)/3) and a thickness (d(µm)) to AxoScan, the following expressions can be calculated.

-   Slow Axis Direction (°)-   Re(λ) = R0(λ)

R0(λ) is expressed as a numerical value calculated by AxoScan andrepresents Re(λ).

The optical element according to the first aspect of the presentinvention is a light reflection element that reflects incident light andincludes a patterned cholesteric liquid crystal layer obtained byimmobilizing a cholesteric liquid crystalline phase.

In the optical element according to the embodiment of the presentinvention, the patterned cholesteric liquid crystal layer has a liquidcrystal alignment pattern in which a direction of an optical axisderived from a liquid crystal compound changes while continuouslyrotating in at least one in-plane direction. Here, in the liquid crystalalignment pattern, a length over which the direction of the optical axisrotates by 180° in the in-plane direction in which the direction of theoptical axis changes while continuously rotating is set as a singleperiod. In addition, the patterned cholesteric liquid crystal layer hasregions having different pitches of helical structures in a plane.

Although described below in detail, the optical element according to theembodiment of the present invention includes the above-describedstructure such that the brightness of emitted light can be made uniformin a case where light propagated in a light guide plate is diffracted bythe optical element to be emitted from the light guide plate.

First Embodiment

FIG. 1 is a diagram conceptually showing an example of the opticalelement according to the embodiment of the present invention.

An optical element 10 shown in the drawing selectively reflects lighthaving a specific wavelength and includes a first reflecting layer 14.

In the optical element 10, the first reflecting layer 14 includes asupport 20, an alignment film 24, and a patterned cholesteric liquidcrystal layer 26.

In addition, the optical element 10 shown in the drawing includes thesupport 20 for the reflecting layer. However, the optical elementaccording to the embodiment of the present invention does notnecessarily include the support 20 for the reflecting layer.

For example, the optical element according to the embodiment of thepresent invention may be formed of only the alignment film and thepatterned cholesteric liquid crystal layer or may be formed of only thepatterned cholesteric liquid crystal layer by peeling off the support 20of the first reflecting layer 14 from the above-described configuration.

That is, the optical element according to the embodiment of the presentinvention can use various layer configurations as long as the patternedcholesteric liquid crystal layer has a liquid crystal alignment patternin which a direction of an optical axis derived from a liquid crystalcompound changes while continuously rotating in at least one in-planedirection and the patterned cholesteric liquid crystal layer has regionshaving different pitches of helical structures in a plane.

The above-described point can be applied to all the optical elementsaccording to respective aspects of the present invention describedbelow.

Support

In the first reflecting layer 14, the support 20 supports the alignmentfilm 24 and the patterned cholesteric liquid crystal layer 26.

As the support 20, various sheet-shaped materials (films or plate-shapedmaterials) can be used as long as they can support the alignment film 24and the patterned cholesteric liquid crystal layer 26.

A transmittance of the support 20 with respect to corresponding light ispreferably 50% or higher, more preferably 70% or higher, and still morepreferably 85% or higher.

The thickness of the support 20 is not particularly limited and may beappropriately set depending on the use of the optical element 10, amaterial for forming the support 20, and the like in a range where thealignment film 24 and the patterned cholesteric liquid crystal layer 26can be supported.

The thickness of the support 20 is preferably 1 to 1000 µm, morepreferably 3 to 250 µm, and still more preferably 5 to 150 µm.

The support 20 may have a single-layer structure or a multi-layerstructure.

In a case where the support 20 has a single-layer structure, examplesthereof include supports formed of glass, triacetyl cellulose (TAC),polyethylene terephthalate (PET), polycarbonates, polyvinyl chloride,acryl, polyolefin, and the like. In a case where the support 20 has amulti-layer structure, examples thereof include a support including: oneof the above-described supports having a single-layer structure that isprovided as a substrate; and another layer that is provided on a surfaceof the substrate.

Alignment Film

In the first reflecting layer 14, the alignment film 24 is formed on asurface of the support 20. The alignment film 24 is an alignment filmfor aligning the liquid crystal compound 30 to a predetermined liquidcrystal alignment pattern during the formation of the patternedcholesteric liquid crystal layer 26 of the first reflecting layer 14.

The following description regarding the alignment film is alsoapplicable to an alignment film provided in the reflection memberdescribed below. Accordingly, in the following description, in a casewhere it is not necessary to distinguish the alignment film from anotheralignment film, the alignment films will also be simply referred to as“alignment film”. In addition, in a case where it is not necessary todistinguish the reflecting layer 14 and the patterned cholesteric liquidcrystal layer 26 from another cholesteric liquid crystal layer, thereflecting layer 14 and the patterned cholesteric liquid crystal layer26 will also be simply referred to as “cholesteric liquid crystallayer”.

Although described below, in the optical element 10 according to theembodiment of the present invention, the patterned cholesteric liquidcrystal layer has a liquid crystal alignment pattern in which adirection of an optical axis 30A (refer to FIG. 2 ) derived from theliquid crystal compound 30 changes while continuously rotating in onein-plane direction.

In addition, in the liquid crystal alignment pattern, a length overwhich the direction of the optical axis 30A rotates by 180° in thein-plane direction in which the direction of the optical axis 30Achanges while continuously rotating is set as a single period A (arotation period of the optical axis).

In the following description, “the direction of the optical axis 30Arotates” will also be simply referred to as “the optical axis 30Arotates”.

As the alignment film, various well-known films can be used.

Examples of the alignment film include a rubbed film formed of anorganic compound such as a polymer, an obliquely deposited film formedof an inorganic compound, a film having a microgroove, and a film formedby lamination of Langmuir-Blodgett (LB) films formed with aLangmuir-Blodgett’s method using an organic compound such asω-tricosanoic acid, dioctadecylmethylammonium chloride, or methylstearate.

The alignment film formed by a rubbing treatment can be formed byrubbing a surface of a polymer layer with paper or fabric in a givendirection multiple times.

As the material used for the alignment film, for example, a material forforming polyimide, polyvinyl alcohol, a polymer having a polymerizablegroup described in JP1997-152509A (JP-H9-152509A), or an alignment filmsuch as JP2005-097377A, JP2005-099228A, and JP2005-128503A ispreferable.

In the optical element 10 according to the embodiment of the presentinvention, for example, the alignment film can be suitably used as aso-called photo-alignment film obtained by irradiating a photo-alignablematerial with polarized light or non-polarized light. That is, in theoptical element 10 according to the embodiment of the present invention,a photo-alignment film that is formed by applying a photo-alignablematerial to the support 20 is suitably used as the alignment film.

The irradiation of polarized light can be performed in a directionperpendicular or oblique to the photo-alignment film, and theirradiation of non-polarized light can be performed in a directionoblique to the photo-alignment film.

Preferable examples of the photo-alignable material used in thephoto-alignment film that can be used in the present invention include:an azo compound described in JP2006-285197A, JP2007-076839A,JP2007-138138A, JP2007-094071A, JP2007-121721A, JP2007-140465A,JP2007-156439A, JP2007-133184A, JP2009-109831A, JP3883848B, andJP4151746B; an aromatic ester compound described in JP2002-229039A; amaleimide- and/or alkenyl-substituted nadiimide compound having aphoto-alignable unit described in JP2002-265541A and JP2002-317013A; aphotocrosslinking silane derivative described in JP4205195B andJP4205198B, a photocrosslinking polyimide, a photocrosslinkingpolyamide, or a photocrosslinking polyester described in JP2003-520878A,JP2004-529220A, and JP4162850B; and a photodimerizable compound, inparticular, a cinnamate compound, a chalcone compound, or a coumarincompound described in JP1997-118717A (JP-H9-118717A), JP1998-506420A(JP-H10-506420A), JP2003-505561A, WO2010/150748A, JP2013-177561A, andJP2014-012823A.

Among these, an azo compound, a photocrosslinking polyimide, aphotocrosslinking polyamide, a photocrosslinking polyester, a cinnamatecompound, or a chalcone compound is suitability used.

The thickness of the alignment film is not particularly limited. Thethickness with which a required alignment function can be obtained maybe appropriately set depending on the material for forming the alignmentfilm.

The thickness of the alignment film is preferably 0.01 to 5 µm and morepreferably 0.05 to 2 µm.

A method of forming the alignment film is not limited. Any one ofvarious well-known methods corresponding to a material for forming thealignment film can be used. For example, a method including: applyingthe alignment film to a surface of the support 20; drying the appliedalignment film; and exposing the alignment film to laser light to forman alignment pattern can be used.

FIG. 4 conceptually shows an example of an exposure device that exposesthe alignment film to form an alignment pattern. In the example shown inFIG. 4 , for example, the exposure of the alignment film 24 of the firstreflecting layer 14 is shown.

An exposure device 60 shown in FIG. 4 includes: a light source 64including a laser 62; an λ/2 plate 65 that changes a polarizationdirection of laser light M emitted from the laser 62; a polarizationbeam splitter 68 that splits the laser light M emitted from the laser 62into two beams MA and MB; mirrors 70A and 70B that are disposed onoptical paths of the splitted two beams MA and MB; and λ/4 plates 72Aand 72B.

Although not shown in the drawing, the light source 64 emits linearlypolarized light P₀. The λ/4 plate 72A converts the linearly polarizedlight P₀ (beam MA) into right circularly polarized light P_(R), and theλ/4 plate 72B converts the linearly polarized light P₀ (beam MB) intoleft circularly polarized light P_(L).

The support 20 including the alignment film 24 on which the alignmentpattern is not yet formed is disposed at an exposed portion, the twobeams MA and MB intersect and interfere each other on the alignment film24, and the alignment film 24 is irradiated with and exposed to theinterference light.

Due to the interference at this time, the polarization state of lightwith which the alignment film 24 is irradiated periodically changesaccording to interference fringes. As a result, in the alignment film24, an alignment pattern in which the alignment state periodicallychanges can be obtained.

In the exposure device 60, by changing an intersection angle α betweenthe two beams MA and MB, the period of the alignment pattern can beadjusted. That is, by adjusting the intersection angle α in the exposuredevice 60, in the alignment pattern in which the optical axis 30Aderived from the liquid crystal compound 30 continuously rotates in thein-plane direction, the length of the single period over which theoptical axis 30A rotates by 180° in the in-plane direction in which theoptical axis 30A rotates can be adjusted.

By forming the cholesteric liquid crystal layer on the alignment filmhaving the alignment pattern in which the alignment state periodicallychanges, as described below, the patterned cholesteric liquid crystallayer 26 having the liquid crystal alignment pattern in which theoptical axis 30A derived from the liquid crystal compound 30continuously rotates in the in-plane direction can be formed.

In addition, by rotating the optical axes of the λ/4 plates 72A and 72Bby 90°, respectively, the rotation direction of the optical axis 30A canbe reversed.

In the optical element according to the embodiment of the presentinvention, the alignment film is provided as a preferable aspect and isnot an essential component.

For example, the following configuration can also be adopted, in which,by forming the alignment pattern on the support 20 using a method ofrubbing the support 20, a method of processing the support 20 with laserlight or the like, or the like, the patterned cholesteric liquid crystallayer has the liquid crystal alignment pattern in which the direction ofthe optical axis 30A derived from the liquid crystal compound 30 changeswhile continuously rotating in at least one in-plane direction.

Patterned Cholesteric Liquid Crystal Layer

In the first reflecting layer 14, the patterned cholesteric liquidcrystal layer 26 is formed on the surface of the alignment film 24.

The patterned cholesteric liquid crystal layer 26 is obtained byimmobilizing a cholesteric liquid crystalline phase, the patternedcholesteric liquid crystal layer has a liquid crystal alignment patternin which a direction of an optical axis derived from a liquid crystalcompound changes while continuously rotating in at least one in-planedirection, and the patterned cholesteric liquid crystal layer hasregions having different pitches of helical structures in a plane.

In FIG. 2 , in order to simplify the drawing and to clarify theconfiguration of the optical element 10, only the liquid crystalcompound 30 (liquid crystal compound molecules) on the surface of thealignment film in the patterned cholesteric liquid crystal layer 26 isconceptually shown. However, as conceptually shown in FIG. 1 , thepatterned cholesteric liquid crystal layer 26 has a helical structure inwhich the liquid crystal compound 30 is helically turned and laminatedas in a cholesteric liquid crystal layer obtained by immobilizing atypical cholesteric liquid crystalline phase. In the helical structure,a configuration in which the liquid crystal compound 30 is helicallyrotated once (rotated by 360) and laminated is set as one helical pitch,and plural pitches of the helically turned liquid crystal compound 30are laminated.

The patterned cholesteric liquid crystal layer has wavelength selectivereflection properties.

For example, in a case where the patterned cholesteric liquid crystallayer 26 has a selective reflection center wavelength in a greenwavelength range, the patterned cholesteric liquid crystal layer 26reflects right circularly polarized light G_(R) of green light andallows transmission of the other light.

Here, since the liquid crystal compound 30 rotates to be aligned in aplane direction, the patterned cholesteric liquid crystal layer 26diffracts (refracts) incident circularly polarized light to be reflectedin a direction in which the direction of the optical axis continuouslyrotates. At this time, the diffraction direction varies depending on theturning direction of incident circularly polarized light.

That is, the patterned cholesteric liquid crystal layer 26 reflectsright circularly polarized light or left circularly polarized lighthaving a selective reflection wavelength and diffracts the reflectedlight.

The patterned cholesteric liquid crystal layer 26 is obtained byimmobilizing a cholesteric liquid crystalline phase. That is, thepatterned cholesteric liquid crystal layer 26 is a layer formed of theliquid crystal compound 30 (liquid crystal material) having acholesteric structure.

Cholesteric Liquid Crystalline Phase

It is known that the cholesteric liquid crystalline phase exhibitsselective reflection properties at a specific wavelength. The centerwavelength λ of selective reflection (selective reflection centerwavelength λ) depends on a pitch P (=helical period) of a helicalstructure in the cholesteric liquid crystalline phase and satisfies arelationship of λ = n × P with an average refractive index n of thecholesteric liquid crystalline phase. Therefore, the selectivereflection center wavelength can be adjusted by adjusting the pitch ofthe helical structure. The pitch of the cholesteric liquid crystallinephase depends on the kind of a chiral agent which is used in combinationof a liquid crystal compound during the formation of the cholestericliquid crystal layer, or the concentration of the chiral agent added.Therefore, a desired pitch can be obtained by adjusting the kind andconcentration of the chiral agent.

The details of the adjustment of the pitch can be found in “Fuji FilmResearch&Development” No. 50 (2005), pp. 60 to 63. As a method ofmeasuring a helical sense and a helical pitch, a method described in“Introduction to Experimental Liquid Crystal Chemistry”, (the JapaneseLiquid Crystal Society, 2007, Sigma Publishing Co., Ltd.), p. 46, and“Liquid Crystal Handbook” (the Editing Committee of Liquid CrystalHandbook, Maruzen Publishing Co., Ltd.), p. 196 can be used.

The cholesteric liquid crystalline phase exhibits selective reflectionproperties with respect to left or circularly polarized light at aspecific wavelength. Whether or not the reflected light is rightcircularly polarized light or left circularly polarized light isdetermined depending on a helical twisted direction (sense) of thecholesteric liquid crystalline phase. Regarding the selective reflectionof the circularly polarized light by the cholesteric liquid crystallinephase, in a case where the helical twisted direction of the cholestericliquid crystalline phase is right, right circularly polarized light isreflected, and in a case where the helical twisted direction of thecholesteric liquid crystalline phase is left, left circularly polarizedlight is reflected.

Accordingly, in the optical element 10 shown in the drawing, thecholesteric liquid crystal layer is a layer obtained by immobilizing aright-twisted cholesteric liquid crystalline phase.

A turning direction of the cholesteric liquid crystalline phase can beadjusted by adjusting the kind of the liquid crystal compound that formsthe cholesteric liquid crystal layer and/or the kind of the chiral agentto be added.

In addition, a half-width Δλ (nm) of a selective reflection range(circularly polarized light reflection range) where selective reflectionis exhibited depends on Δn of the cholesteric liquid crystalline phaseand the helical pitch P and complies with a relationship of Δλ = Δn × P.Therefore, the width of the selective reflection range can be controlledby adjusting Δn. Δn can be adjusted by adjusting a kind of a liquidcrystal compound for forming the cholesteric liquid crystal layer and amixing ratio thereof, and a temperature during alignment immobilization.

The half-width of the reflection wavelength range is adjusted dependingon the application of the optical element 10 and is, for example, 10 to500 nm and preferably 20 to 300 nm and more preferably 30 to 100 nm.

Method of Forming Cholesteric Liquid Crystal Layer

The cholesteric liquid crystal layer (patterned cholesteric liquidcrystal layer) can be formed by immobilizing a cholesteric liquidcrystalline phase in a layer shape.

The structure in which a cholesteric liquid crystalline phase isimmobilized may be a structure in which the alignment of the liquidcrystal compound as a cholesteric liquid crystalline phase isimmobilized. Typically, the structure in which a cholesteric liquidcrystalline phase is immobilized is preferably a structure which isobtained by making the polymerizable liquid crystal compound to be in astate where a cholesteric liquid crystalline phase is aligned,polymerizing and curing the polymerizable liquid crystal compound withultraviolet irradiation, heating, or the like to form a layer having nofluidity, and concurrently changing the state of the polymerizableliquid crystal compound into a state where the aligned state is notchanged by an external field or an external force.

The structure in which a cholesteric liquid crystalline phase isimmobilized is not particularly limited as long as the opticalcharacteristics of the cholesteric liquid crystalline phase aremaintained, and the liquid crystal compound 30 in the cholesteric liquidcrystal layer does not necessarily exhibit liquid crystallinity. Forexample, the molecular weight of the polymerizable liquid crystalcompound may be increased by a curing reaction such that the liquidcrystallinity thereof is lost.

Examples of a material used for forming the cholesteric liquid crystallayer obtained by immobilizing a cholesteric liquid crystalline phaseinclude a liquid crystal composition including a liquid crystalcompound. It is preferable that the liquid crystal compound is apolymerizable liquid crystal compound.

In addition, the liquid crystal composition used for forming thecholesteric liquid crystal layer may further include a surfactant and achiral agent.

Polymerizable Liquid Crystal Compound

The polymerizable liquid crystal compound may be a rod-shaped liquidcrystal compound or a disk-shaped liquid crystal compound.

Examples of the rod-shaped polymerizable liquid crystal compound forforming the cholesteric liquid crystalline phase include a rod-shapednematic liquid crystal compound. As the rod-shaped nematic liquidcrystal compound, an azomethine compound, an azoxy compound, acyanobiphenyl compound, a cyanophenyl ester compound, a benzoatecompound, a phenyl cyclohexanecarboxylate compound, acyanophenylcyclohexane compound, a cyano-substituted phenylpyrimidinecompound, an alkoxy-substituted phenylpyrimidine compound, aphenyldioxane compound, a tolan compound, or analkenylcyclohexylbenzonitrile compound is preferably used. Not only alow-molecular-weight liquid crystal compound but also ahigh-molecular-weight liquid crystal compound can be used.

The polymerizable liquid crystal compound can be obtained by introducinga polymerizable group into the liquid crystal compound. Examples of thepolymerizable group include an unsaturated polymerizable group, an epoxygroup, and an aziridinyl group. Among these, an unsaturatedpolymerizable group is preferable, and an ethylenically unsaturatedpolymerizable group is more preferable. The polymerizable group can beintroduced into the molecules of the liquid crystal compound usingvarious methods. The number of polymerizable groups in the polymerizableliquid crystal compound is preferably 1 to 6 and more preferably 1 to 3.

Examples of the polymerizable liquid crystal compound include compoundsdescribed in Makromol. Chem. (1989), Vol. 190, p. 2255, AdvancedMaterials (1993), Vol. 5, p. 107, US4683327A, US5622648A, US5770107A,WO95/022586, WO95/024455, WO97/000600, WO98/023580, WO98/052905,JP1989-272551A(JP-H1-272551A), JP1994-016616A (JP-H6-016616A),JP1995-110469A (JP-H7-110469A), JP1999-080081A (JP-H11-080081A), andJP2001-328973A. Two or more polymerizable liquid crystal compounds maybe used in combination. In a case where two or more polymerizable liquidcrystal compounds are used in combination, the alignment temperature canbe decreased.

In addition, as a polymerizable liquid crystal compound other than theabove-described examples, for example, a cyclic organopolysiloxanecompound having a cholesteric phase described in JP1982-165480A(JP-S57-165480A) can be used. Further, as the above-describedhigh-molecular-weight liquid crystal compound, for example, a polymer inwhich a liquid crystal mesogenic group is introduced into a main chain,a side chain, or both a main chain and a side chain, a polymercholesteric liquid crystal in which a cholesteryl group is introducedinto a side chain, a liquid crystal polymer described in JP1997-133810A(JP-H9-133810A), and a liquid crystal polymer described inJP1999-293252A (JP-H1 1-293252A) can be used.

Disk-Shaped Liquid Crystal Compound

As the disk-shaped liquid crystal compound, for example, compoundsdescribed in JP2007-108732A and JP2010-244038A can be preferably used.

In addition, the addition amount of the polymerizable liquid crystalcompound in the liquid crystal composition is preferably 75% to 99.9mass%, more preferably 80% to 99 mass%, and still more preferably 85% to90 mass% with respect to the solid content mass (mass excluding asolvent) of the liquid crystal composition.

Surfactant

The liquid crystal composition used for forming the cholesteric liquidcrystal layer may include a surfactant.

It is preferable that the surfactant is a compound that can function asan alignment controller contributing to the stable or rapid formation ofa cholesteric liquid crystalline phase with planar alignment. Examplesof the surfactant include a silicone surfactant and a fluorinesurfactant. Among these, a fluorine surfactant is preferable.

Specific examples of the surfactant include compounds described inparagraphs “0082” to “0090” of JP2014-119605A, compounds described inparagraphs “0031” to “0034” of JP2012-203237A, exemplary compoundsdescribed in paragraphs “0092” and “0093” of JP2005-099248A, exemplarycompounds described in paragraphs “0076” to “0078” and paragraphs “0082”to “0085” of JP2002-129162A, and fluorine (meth)acrylate polymersdescribed in paragraphs “0018” to “0043” of JP2007-272185A.

As the surfactant, one kind may be used alone, or two or more kinds maybe used in combination.

As the fluorine surfactant, a compound described in paragraphs “0082” to“0090” of JP2014-119605A is preferable.

The addition amount of the surfactant in the liquid crystal compositionis preferably 0.01 to 10 mass%, more preferably 0.01 to 5 mass%, andstill more preferably 0.02 to 1 mass% with respect to the total mass ofthe liquid crystal compound.

Chiral Agent (Optically Active Compound)

The chiral agent has a function of causing a helical structure of acholesteric liquid crystalline phase to be formed. The chiral agent maybe selected depending on the purpose because a helical twisted directionor a helical pitch derived from the compound varies.

The chiral agent is not particularly limited, and a well-known compound(for example, Liquid Crystal Device Handbook (No. 142 Committee of JapanSociety for the Promotion of Science, 1989), Chapter 3, Article 4-3,chiral agent for turned nematic (TN) or super turned nematic (STN), p.199), isosorbide, or an isomannide derivative can be used.

In general, the chiral agent includes an asymmetric carbon atom.However, an axially asymmetric compound or a surface asymmetric compoundnot having an asymmetric carbon atom can also be used as a chiral agent.Examples of the axially asymmetric compound or the surface asymmetriccompound include binaphthyl, helicene, paracyclophane, and derivativesthereof. The chiral agent may include a polymerizable group. In a casewhere both the chiral agent and the liquid crystal compound have apolymerizable group, a polymer which includes a repeating unit derivedfrom the polymerizable liquid crystal compound and a repeating unitderived from the chiral agent can be formed due to a polymerizationreaction of a polymerizable chiral agent and the polymerizable liquidcrystal compound. In this aspect, it is preferable that thepolymerizable group included in the polymerizable chiral agent is thesame as the polymerizable group included in the polymerizable liquidcrystal compound. Accordingly, the polymerizable group of the chiralagent is preferably an unsaturated polymerizable group, an epoxy group,or an aziridinyl group, more preferably an unsaturated polymerizablegroup, and still more preferably an ethylenically unsaturatedpolymerizable group.

In addition, the chiral agent may be a liquid crystal compound.

In a case where the chiral agent includes a photoisomerization group, apattern having a desired reflection wavelength corresponding to anemission wavelength can be formed by irradiation of an actinic ray orthe like through a photomask after coating and alignment, which ispreferable. As the photoisomerization group, an isomerization portion ofa photochromic compound, an azo group, an azoxy group, or a cinnamoylgroup is preferable. Specific examples of the compound include compoundsdescribed in JP2002-080478A, JP2002-080851A, JP2002-179668A,JP2002-179669A, JP2002-179670A, JP2002-179681A, JP2002-179682A,JP2002-338575A, JP2002-338668A, JP2003-313189A, and JP2003-313292A.

Photoreactive Chiral Agent

In the present invention, it is preferable that a photoreactive chiralagent is used as the chiral agent. The photoreactive chiral agent isformed of, for example, a compound represented by the following Formula(I) and has properties capable of controlling an aligned structure ofthe liquid crystal compound and changing a helical pitch of liquidcrystal, that is, a helical twisting power (HTP) of a helical structureduring light irradiation. That is, the photoreactive chiral agent is acompound that causes a helical twisting power of a helical structurederived from a liquid crystal compound, preferably, a nematic liquidcrystal compound to change during light irradiation (ultraviolet lightto visible light to infrared light), and includes a portion including achiral portion and a portion in which a structural change occurs duringlight irradiation as necessary portions (molecular structural units).However, the photoreactive chiral agent represented by the followingFormula (I) can significantly change the HTP of liquid crystalmolecules.

The above-described HTP represents the helical twisting power of ahelical structure of liquid crystal, that is, HTP = 1/(Pitch × ChiralAgent Concentration [Mass Fraction]). For example, the HTP can beobtained by measuring a helical pitch (single period of the helicalstructure; µm) of a liquid crystal molecule at a given temperature andconverting the measured value into a value [µm⁻¹] in terms of theconcentration of the chiral agent. In a case where a selectivereflection color is formed by the photoreactive chiral agent dependingon the illuminance of light, a change ratio in HTP (HTP beforeirradiation/HTP after irradiation) is preferably 1.5 or higher and morepreferably 2.5 or higher in a case where the HTP decreases afterirradiation, and is preferably 0.7 or lower and more preferably 0.4 orlower in a case where the HTP increases after irradiation.

Next, the compound represented by Formula (I) will be described.

In the formula, R represents a hydrogen atom, an alkoxy group having 1to 15 carbon atoms, an acryloyloxyalkyloxy group having 3 to 15 carbonatoms in total, or a methacryloyloxyalkyloxy group having 4 to 15 carbonatoms in total.

Examples of the alkoxy group having 1 to 15 carbon atoms include amethoxy group, an ethoxy group, a propoxy group, a butoxy group, ahexyloxy group, and a dodecyloxy group. In particular, an alkoxy grouphaving 1 to 12 carbon atoms is preferable, and an alkoxy group having 1to 8 carbon atoms is more preferable.

Examples of the acryloyloxyalkyloxy group having 3 to 15 carbon atoms intotal include an acryloyloxyethyloxy group, an acryloyloxybutyloxygroup, and an acryloyloxydecyloxy group. In particular, anacryloyloxyalkyloxy group having 5 to 13 carbon atoms is preferable, andan acryloyloxyalkyloxy group having 5 to 11 carbon atoms is morepreferable.

Examples of the methacryloyloxyalkyloxy group having 4 to 15 carbonatoms in total include a methacryloyloxyethyloxy group, amethacryloyloxybutyloxy group, and a methacryloyloxydecyloxy group. Inparticular, a methacryloyloxyalkyloxy group having 6 to 14 carbon atomsis preferable, and a methacryloyloxyalkyloxy group having 6 to 12 carbonatoms is more preferable.

The molecular weight of the photoreactive chiral agent represented byFormula (I) is preferably 300 or higher. In addition, it is preferablethat the solubility in the liquid crystal compound described below ishigh, and it is more preferable that the solubility parameter SP valueis close to that of the liquid crystal compound.

Hereinafter, specific examples (exemplary compounds (1) to (15)) of thecompound represented by Formula (I) will be shown, but the presentinvention is not limited thereto.

In the present invention, as the photoreactive chiral agent, forexample, a photoreactive optically active compound represented by thefollowing Formula (II) is also used.

In the formula, R represents a hydrogen atom, an alkoxy group having 1to 15 carbon atoms, an acryloyloxyalkyloxy group having 3 to 15 carbonatoms in total, or a methacryloyloxyalkyloxy group having 4 to 15 carbonatoms in total.

Examples of the alkoxy group having 1 to 15 carbon atoms include amethoxy group, an ethoxy group, a propoxy group, a butoxy group, ahexyloxy group, an octyloxy group, and a dodecyloxy group. Inparticular, an alkoxy group having 1 to 10 carbon atoms is preferable,and an alkoxy group having 1 to 8 carbon atoms is more preferable.

Examples of the acryloyloxyalkyloxy group having 3 to 15 carbon atoms intotal include an acryloyloxy group, an acryloyloxyethyloxy group, anacryloyloxypropyloxy group, an acryloyloxyhexyloxy group, anacryloyloxybutyloxy group, and an acryloyloxydecyloxy group. Inparticular, an acryloyloxyalkyloxy group having 3 to 13 carbon atoms ispreferable, and an acryloyloxyalkyloxy group having 3 to 11 carbon atomsis more preferable.

Examples of the methacryloyloxyalkyloxy group having 4 to 15 carbonatoms in total include a methacryloyloxy group, amethacryloyloxyethyloxy group, and a methacryloyloxyhexyloxy group. Inparticular, a methacryloyloxyalkyloxy group having 4 to 14 carbon atomsis preferable, and a methacryloyloxyalkyloxy group having 4 to 12 carbonatoms is more preferable.

The molecular weight of the photoreactive optically active compoundrepresented by Formula (II) is preferably 300 or higher. In addition, itis preferable that the solubility in the liquid crystal compounddescribed below is high, and it is more preferable that the solubilityparameter SP value is close to that of the liquid crystal compound.

Hereinafter, specific examples (exemplary compounds (21) to (32)) of thephotoreactive optically active compound represented by Formula (II) willbe shown, but the present invention is not limited thereto.

In addition, the photoreactive chiral agent can also be used incombination with a chiral agent having no photoreactivity such as achiral compound having a large temperature dependence of the helicaltwisting power. Examples of the well-known chiral agent having nophotoreactivity include chiral agents described in JP2000-044451A,JP1998-509726A (JP-H10-509726A), WO1998/000428A, JP2000-506873A,JP1997-506088A(JP-H09-506088A), Liquid Crystals (1996, 21, 327), andLiquid Crystals (1998, 24, 219).

The content of the chiral agent in the liquid crystal composition ispreferably 0.01% to 200 mol% and more preferably 1% to 30 mol% withrespect to the content molar amount of the liquid crystal compound.

Polymerization Initiator

In a case where the liquid crystal composition includes a polymerizablecompound, it is preferable that the liquid crystal composition includesa polymerization initiator. In an aspect where a polymerization reactionprogresses with ultraviolet irradiation, it is preferable that thepolymerization initiator is a photopolymerization initiator whichinitiates a polymerization reaction with ultraviolet irradiation.

Examples of the photopolymerization initiator include an α-carbonylcompound (described in US2367661A and US2367670A), an acyloin ether(described in US2448828A), an α-hydrocarbon-substituted aromatic acyloincompound (described in US2722512A), a polynuclear quinone compound(described in US3046127A and US2951758A), a combination of atriarylimidazole dimer and p-aminophenyl ketone (described inUS3549367A), an acridine compound and a phenazine compound (described inJP1985-105667A (JP-S60-105667A) and US4239850A), and an oxadiazolecompound (described in US4212970A).

The content of the photopolymerization initiator in the liquid crystalcomposition is preferably 0.1 to 20 mass% and more preferably 0.5 to 12mass% with respect to the content of the liquid crystal compound.

Crosslinking Agent

In order to improve the film hardness after curing and to improvedurability, the liquid crystal composition may optionally include acrosslinking agent. As the crosslinking agent, a curing agent which canperform curing with ultraviolet light, heat, moisture, or the like canbe preferably used.

The crosslinking agent is not particularly limited and can beappropriately selected depending on the purpose. Examples of thecrosslinking agent include: a polyfunctional acrylate compound such astrimethylol propane tri(meth)acrylate or pentaerythritoltri(meth)acrylate; an epoxy compound such as glycidyl (meth)acrylate orethylene glycol diglycidyl ether; an aziridine compound such as 2,2-bishydroxymethyl butanol-tris[3-(1-aziridinyl)propionate] or4,4-bis(ethyleneiminocarbonylamino)diphenylmethane; an isocyanatecompound such as hexamethylene diisocyanate or a biuret type isocyanate;a polyoxazoline compound having an oxazoline group at a side chainthereof; and an alkoxysilane compound such as vinyl trimethoxysilane orN-(2-aminoethyl)-3-aminopropyltrimethoxysilane. In addition, dependingon the reactivity of the crosslinking agent, a well-known catalyst canbe used, and not only film hardness and durability but also productivitycan be improved. Among these crosslinking agents, one kind may be usedalone, or two or more kinds may be used in combination.

The content of the crosslinking agent is preferably 3% to 20 mass% andmore preferably 5% to 15 mass% with respect to the solid content mass ofthe liquid crystal composition. In a case where the content of thecrosslinking agent is in the above-described range, an effect ofimproving a crosslinking density can be easily obtained, and thestability of a cholesteric liquid crystalline phase is further improved.

Other Additives

Optionally, a polymerization inhibitor, an antioxidant, an ultravioletabsorber, a light stabilizer, a coloring material, metal oxideparticles, or the like can be added to the liquid crystal composition ina range where optical performance and the like do not deteriorate.

In a case where the cholesteric liquid crystal layer is formed, it ispreferable that the liquid crystal composition is used as liquid.

The liquid crystal composition may include a solvent. The solvent is notparticularly limited and can be appropriately selected depending on thepurpose. An organic solvent is preferable.

The organic solvent is not particularly limited and can be appropriatelyselected depending on the purpose. Examples of the organic solventinclude a ketone, an alkyl halide, an amide, a sulfoxide, a heterocycliccompound, a hydrocarbon, an ester, and an ether. Among these organicsolvents, one kind may be used alone, or two or more kinds may be usedin combination. Among these, a ketone is preferable in consideration ofan environmental burden.

In a case where the cholesteric liquid crystal layer is formed, it ispreferable that the cholesteric liquid crystal layer is formed byapplying the liquid crystal composition to a surface where thecholesteric liquid crystal layer is to be formed, aligning the liquidcrystal compound to a state of a cholesteric liquid crystalline phase,and curing the liquid crystal compound.

That is, in a case where the cholesteric liquid crystal layer is formedon the alignment film, it is preferable that the cholesteric liquidcrystal layer obtained by immobilizing a cholesteric liquid crystallinephase is formed by applying the liquid crystal composition to thealignment film, aligning the liquid crystal compound to a state of acholesteric liquid crystalline phase, and curing the liquid crystalcompound.

For the application of the liquid crystal composition, a printing methodsuch as ink jet or scroll printing or a well-known method such as spincoating, bar coating, or spray coating capable of uniformly applyingliquid to a sheet-shaped material can be used.

The applied liquid crystal composition is optionally dried and/or heatedand then is cured to form the cholesteric liquid crystal layer. In thedrying and/or heating step, the liquid crystal compound in the liquidcrystal composition only has to be aligned to a cholesteric liquidcrystalline phase. In the case of heating, the heating temperature ispreferably 200° C. or lower and more preferably 130° C. or lower.

The aligned liquid crystal compound is optionally further polymerized.Regarding the polymerization, thermal polymerization orphotopolymerization using light irradiation may be performed, andphotopolymerization is preferable. Regarding the light irradiation,ultraviolet light is preferably used. The irradiation energy ispreferably 20 mJ/cm² to 50 J/cm² and more preferably 50 to 1500 mJ/cm².In order to promote a photopolymerization reaction, light irradiationmay be performed under heating conditions or in a nitrogen atmosphere.The wavelength of irradiated ultraviolet light is preferably 250 to 430nm.

The thickness of the cholesteric liquid crystal layer is notparticularly limited, and the thickness with which a required lightreflectivity can be obtained may be appropriately set depending on theuse of the optical element 10, the light reflectivity required for thecholesteric liquid crystal layer, the material for forming thecholesteric liquid crystal layer, and the like.

Liquid Crystal Alignment Pattern of Patterned Cholesteric Liquid CrystalLayer

In the optical element 10 according to the embodiment of the presentinvention, the patterned cholesteric liquid crystal layer has the liquidcrystal alignment pattern in which the direction of the optical axis 30Aderived from the liquid crystal compound 30 forming the cholestericliquid crystalline phase changes while continuously rotating in thein-plane direction of the patterned cholesteric liquid crystal layer.

The optical axis 30A derived from the liquid crystal compound 30 is anaxis having the highest refractive index in the liquid crystal compound30, that is, a so-called slow axis. For example, in a case where theliquid crystal compound 30 is a rod-shaped liquid crystal compound, theoptical axis 30A is along a rod-shaped major axis direction. In thefollowing description, the optical axis 30A derived from the liquidcrystal compound 30 will also be referred to as “the optical axis 30A ofthe liquid crystal compound 30” or “the optical axis 30A”.

FIG. 2 is a plan view conceptually showing the patterned cholestericliquid crystal layer 26.

The plan view is a view in a case where the optical element 10 is seenfrom the top in FIG. 1 , that is, a view in a case where the opticalelement 10 is seen from a thickness direction (laminating direction ofthe respective layers (films)).

In addition, as described above, in FIG. 2 , in order to clarify theconfiguration of the optical element 10 according to the embodiment ofthe present invention, only the liquid crystal compound 30 on thesurface of the alignment film 24 is shown.

FIG. 2 shows the patterned cholesteric liquid crystal layer 26 as arepresentative example. However, basically, a patterned cholestericliquid crystal layer described below also has the same configuration andthe same effects as those of the patterned cholesteric liquid crystallayer 26, except that the lengths A of the single periods of the liquidcrystal alignment patterns described below or the reflection wavelengthranges are different from each other.

As shown in FIG. 2 , on the surface of the alignment film 24, the liquidcrystal compound 30 forming the patterned cholesteric liquid crystallayer 26 is two-dimensionally arranged according to the alignmentpattern formed on the alignment film 24 as the lower layer in apredetermined in-plane direction indicated by arrow X and a directionperpendicular to the in-plane direction (arrow X direction).

In the following description, the direction perpendicular to the arrow Xdirection will be referred to as “Y direction” for convenience ofdescription. That is, in FIG. 1 and FIG. 3 described below, the Ydirection is a direction perpendicular to the paper plane.

In addition, the liquid crystal compound 30 forming the patternedcholesteric liquid crystal layer 26 has the liquid crystal alignmentpattern in which the direction of the optical axis 30A changes whilecontinuously rotating in the arrow X direction in a plane of thepatterned cholesteric liquid crystal layer 26. In the example shown inthe drawing, the liquid crystal compound 30 has the liquid crystalalignment pattern in which the optical axis 30A of the liquid crystalcompound 30 changes while continuously rotating clockwise in the arrow Xdirection.

Specifically, “the direction of the optical axis 30A of the liquidcrystal compound 30 changes while continuously rotating in the arrow Xdirection (the predetermined in-plane direction)” represents that anangle between the optical axis 30A of the liquid crystal compound 30,which is arranged in the arrow X direction, and the arrow X directionvaries depending on positions in the arrow X direction, and the anglebetween the optical axis 30A and the arrow X direction sequentiallychanges from θ to θ+180° or θ-180° in the arrow X direction.

A difference between the angles of the optical axes 30A of the liquidcrystal compound 30 adjacent to each other in the arrow X direction ispreferably 45° or less, more preferably 15° or less, and still morepreferably less than 15°.

On the other hand, in the liquid crystal compound 30 forming thepatterned cholesteric liquid crystal layer 26, the directions of theoptical axes 30A are the same in the Y direction perpendicular to thearrow X direction, that is, the Y direction perpendicular to thein-plane direction in which the optical axis 30A continuously rotates.

In other words, in the liquid crystal compound 30 forming the patternedcholesteric liquid crystal layer 26, angles between the optical axes 30Aof the liquid crystal compound 30 and the arrow X direction are the samein the Y direction.

In the optical element 10 according to the embodiment of the presentinvention, in the liquid crystal alignment pattern of the liquid crystalcompound 30, the length (distance) over which the optical axis 30A ofthe liquid crystal compound 30 rotates by 180° in the arrow X directionin which the optical axis 30A changes while continuously rotating in aplane is the length A of the single period in the liquid crystalalignment pattern.

That is, a distance between centers of two liquid crystal compounds 30in the arrow X direction is the length A of the single period, the twoliquid crystal compounds having the same angle in the arrow X direction.Specifically, as shown in FIG. 2 , a distance of centers in the arrow Xdirection of two liquid crystal compounds 30 in which the arrow Xdirection and the direction of the optical axis 30A match each other isthe length A of the single period.

In the following description, the length A of the single period willalso be referred to as “single period A”.

In the optical element 10 according to the embodiment of the presentinvention, in the liquid crystal alignment pattern of the patternedcholesteric liquid crystal layer, the single period A is repeated in thearrow X direction, that is, in the in-plane direction in which thedirection of the optical axis 30A changes while continuously rotating.

The patterned cholesteric liquid crystal layer 26 has the liquid crystalalignment pattern in which the optical axis 30A changes whilecontinuously rotating in the arrow X direction in a plane (thepredetermined in-plane direction).

The cholesteric liquid crystal layer obtained by immobilizing acholesteric liquid crystalline phase typically reflects incident light(circularly polarized light) by specular reflection.

On the other hand, the patterned cholesteric liquid crystal layer 26having the above-described liquid crystal alignment pattern reflectsincidence light in a direction having an angle in the arrow X directionwith respect to specular reflection. For example, in the patternedcholesteric liquid crystal layer 26, light incident from the normaldirection is reflected in a state where it is tilted as indicated by thearrow X with respect to the normal direction instead of being reflectedin the normal direction. That is, the light incident from the normaldirection refers to light incident from the front side that is lightincident to be perpendicular to a main surface. The main surface refersto the maximum surface of a sheet-shaped material.

Hereinafter, the description will be made with reference to FIG. 3 .

As described above, the patterned cholesteric liquid crystal layer 26selectively reflects one circularly polarized light in a selectivereflection wavelength. For example, a case where the selectivereflection wavelength of the patterned cholesteric liquid crystal layer26 is green light and right circularly polarized light is reflected willbe described. The patterned cholesteric liquid crystal layer 26selectively reflects right circularly polarized light G_(R) of greenlight.

Accordingly, in a case where light is incident into the first reflectinglayer 14, the patterned cholesteric liquid crystal layer 26 reflectsonly right circularly polarized light G_(R) of green light and allowstransmission of the other light.

In a case where the right circularly polarized light G_(R) of greenlight incident into the patterned cholesteric liquid crystal layer 26 isreflected from the patterned cholesteric liquid crystal layer 26, theabsolute phase changes depending on the directions of the optical axes30A of the respective liquid crystal compounds 30.

Here, in the patterned cholesteric liquid crystal layer 26, the opticalaxis 30A of the liquid crystal compound 30 changes while rotating in thearrow X direction (the in-plane direction). Therefore, the amount ofchange in the absolute phase of the incident right circularly polarizedlight G_(R) of green light varies depending on the directions of theoptical axes 30A.

Further, the liquid crystal alignment pattern formed in the patternedcholesteric liquid crystal layer 26 is a pattern that is periodic in thearrow X direction. Therefore, as conceptually shown in FIG. 3 , anabsolute phase Q that is periodic in the arrow X direction correspondingto the direction of the optical axis 30A is assigned to the rightcircularly polarized light G_(R) of green light incident into thepatterned cholesteric liquid crystal layer 26.

In addition, the direction of the optical axis 30A of the liquid crystalcompound 30 with respect to the arrow X direction is uniform in thearrangement of the liquid crystal compound 30 in the Y directionperpendicular to arrow X direction.

As a result, in the patterned cholesteric liquid crystal layer 26, anequiphase surface E that is tilted in the arrow X direction with respectto an XY plane is formed for the right circularly polarized light G_(R)of green light.

Therefore, the right circularly polarized light G_(R) of green light isreflected in the normal direction of the equiphase surface E (directionperpendicular to the equiphase surface E), and the reflected rightcircularly polarized light G_(R) of green light is reflected in adirection that is tilted in the arrow X direction with respect to the XYplane (main surface of the patterned cholesteric liquid crystal layer26).

Here, a reflection angle of light from the patterned cholesteric liquidcrystal layer in which the optical axis 30A of the liquid crystalcompound 30 continuously rotates in the in-plane direction (arrow Xdirection) varies depending on wavelengths of light to be reflected.Specifically, as the wavelength of light increases, the angle ofreflected light with respect to incidence light increases.

On the other hand, a reflection angle of light from the patternedcholesteric liquid crystal layer in which the optical axis 30A of theliquid crystal compound 30 continuously rotates in the arrow X direction(in-plane direction) varies depending on the length A of the singleperiod of the liquid crystal alignment pattern over which the opticalaxis 30A rotates by 180° in the arrow X direction, that is, depending onthe single period A. Specifically, as the length of the single period Adecreases, the angle of reflected light with respect to incidence lightincrease s.

In the optical element 10 according to the embodiment of the presentinvention, the single period A in the alignment pattern of the patternedcholesteric liquid crystal layer is not particularly limited and may beappropriately set depending on the use of the optical element 10 and thelike.

Here, the optical element 10 according to the embodiment of the presentinvention can be suitably used as, for example, a diffraction elementthat reflects light displayed by a display to be introduced into a lightguide plate in AR glasses or a diffraction element that reflects lightpropagated in a light guide plate to be emitted to an observationposition by a user from the light guide plate.

At this time, in order to totally reflect light from the light guideplate, it is necessary to reflect light to be introduced into the lightguide plate at a large angle to some degree with respect to incidencelight. In addition, in order to reliably emit light propagated in thelight guide plate, it is necessary to reflect at a large angle to somedegree with respect to incidence light.

In addition, as described above, the reflection angle from the patternedcholesteric liquid crystal layer with respect to incidence light can beincreased by reducing the single period A in the liquid crystalalignment pattern.

In consideration of this point, the single period A in the liquidcrystal alignment pattern of the patterned cholesteric liquid crystallayer is preferably 50 µm or less, more preferably 10 µm or less, andstill more preferably 1 µm or less.

In consideration of the accuracy of the liquid crystal alignment patternand the like, the single period A in the liquid crystal alignmentpattern of the patterned cholesteric liquid crystal layer is preferably0.1 µm or more.

Here, in the optical element according to the embodiment of the presentinvention, the patterned cholesteric liquid crystal layer has the liquidcrystal alignment pattern in which the direction of the optical axis 30Aderived from the liquid crystal compound 30 forming the cholestericliquid crystalline phase changes while continuously rotating in thein-plane direction of the patterned cholesteric liquid crystal layer.

In addition, in the optical element according to the embodiment of thepresent invention, as conceptually shown in FIG. 1 , the patternedcholesteric liquid crystal layer has regions having different pitches ofhelical structures in a plane.

The optical element 10 shown in FIG. 1 is configured such that thepatterned cholesteric liquid crystal layer 26 of the first reflectinglayer 14 has a liquid crystal alignment pattern in which a direction ofan optical axis derived from a liquid crystal compound changes whilecontinuously rotating in at least one in-plane direction (hereinafter,referred to as “in-plane direction in which the optical axis rotates”)and such that a pitch of a helical structure (hereinafter, referred toas “helical pitch”) in the patterned cholesteric liquid crystal layerincreases from one side toward another side in the in-plane direction inwhich the optical axis rotates.

Specifically, the patterned cholesteric liquid crystal layer 26 in FIG.1 is configured such that a helical pitch PT₁ in the right side regionof FIG. 1 is longer than a helical pitch PT₂ in the left side region ofFIG. 1 and the helical pitch increases from the left side region towardthe right side region in FIG. 1 .

The helical pitch is the distance over which the liquid crystal compoundrotates helically once (360° rotation). In FIG. 1 , schematically,distances over which the liquid crystal compound rotates half a rotation(180° rotation) are represented by PT₁ and PT₂.

The optical element according to the embodiment of the present inventionhas the above-described configuration such that, in a light guideelement used in an AR display device or the like of augmented reality(AR) glasses or the like, in a case where the optical element accordingto the embodiment of the present invention is used as a diffractionelement that diffracts light propagated in a light guide plate to beemitted from the light guide plate, the diffraction efficiency can bechanged to increase in the light propagation direction (refer to FIG. 5). Therefore, even in a case where exit pupil expansion is performed,the brightness (light amount) of light emitted from the light guideplate can be made uniform.

Specifically, in a case where the selective reflection wavelength of thepatterned cholesteric liquid crystal layer 26 is represented by λ_(a),the patterned cholesteric liquid crystal layer 26 can reflect light ator near the selective reflection wavelength λ_(a). The reflectionefficiency from the patterned cholesteric liquid crystal layer 26 is thehighest at the selective reflection wavelength λ_(a), and as thewavelength of light incident into the patterned cholesteric liquidcrystal layer 26 becomes distant from the selective reflectionwavelength λ_(a), the reflection efficiency from the patternedcholesteric liquid crystal layer 26 decreases. Therefore, thediffraction efficiency from the patterned cholesteric liquid crystallayer 26 is also the highest at the selective reflection wavelengthλ_(a), and as the wavelength of light incident into the patternedcholesteric liquid crystal layer 26 becomes distant from the selectivereflection wavelength λ_(a), the diffraction efficiency from thepatterned cholesteric liquid crystal layer 26 decreases.

Accordingly, in the patterned cholesteric liquid crystal layer, thehelical pitch changes from one side toward another side in the in-planedirection in which the optical axis rotates such that the diffractionefficiency can be changed.

For example, in a case where the optical element according to theembodiment of the present invention is used as a diffraction element ofa light guide element used in an AR display device or the like, in thepatterned cholesteric liquid crystal layer, the helical pitch increasesfrom one side toward another side in the in-plane direction in which theoptical axis rotates. As a result, as shown in FIG. 5 , a configurationthe diffraction efficiency increases from one side toward another sidein the in-plane direction in which the optical axis rotates can beadopted.

This way, in the patterned cholesteric liquid crystal layer, thediffraction efficiency increases from one side toward another side inthe in-plane direction in which the optical axis rotates. As a result,even in a case where exit pupil expansion is performed in a light guideelement used in an AR display device or the like, the brightness (lightamount) of light emitted from a light guide plate can be made uniform.

This point will be described below.

Here, the diffraction efficiency refers to a ratio of the amount ofdiffracted light to the amount of light incident into a diffractionelement. The patterned cholesteric liquid crystal layer 26 istransferred to a dove prism 120 (refractive index=1.517, slopeangle=45°) as shown in FIG. 11 , laser light having a predeterminedwavelength is caused to transmit through a linear polarizer 122 and aλ/4 plate 124 to be converted into right circularly polarized light, andthe right circularly polarized light is caused to be incident into thesurface of the patterned cholesteric liquid crystal layer 26 with anangle that is set such that diffracted light is emitted vertically fromthe slope. An emitted light intensity Lr is measured using a Power Meter1918-C (manufactured by Newport Corporation), and a ratio (Lr/Li × 100[%]) of the emitted light intensity Lr to an incidence light intensityLi is obtained as a diffraction efficiency.

In the patterned cholesteric liquid crystal layer in which thediffraction efficiency changes in the in-plane direction in which theoptical axis rotates, a helical pitch of a region having a highdiffraction efficiency may be set as a helical pitch of a selectivereflection wavelength close to a wavelength of light to be reflected anddiffracted. In addition, a helical pitch of a region having a lowdiffraction efficiency may be set as a helical pitch of a selectivereflection wavelength distant from a wavelength of light to be reflectedand diffracted. At this time, the helical pitch may be longer or shorterthan the helical pitch of the selective reflection wavelength.

In addition, in a case where a direction in which regions having aconstant helical pitch are arranged in the patterned cholesteric liquidcrystal layer is set as a change direction of helical pitch, The changedirection of helical pitch may be the same as or different from thein-plane direction in which the optical axis rotates. That is, thechange direction of helical pitch may intersect the in-plane directionin which the optical axis rotates. Even in the configuration in whichthe change direction of helical pitch intersects the in-plane directionin which the optical axis rotates, the helical pitch changes (increases)from one side toward another side in the in-plane direction in which theoptical axis rotates.

In the patterned cholesteric liquid crystal layer (cholesteric liquidcrystal layer) according to the embodiment of the present inventionhaving a liquid crystal alignment pattern in which a direction of anoptical axis derived from a liquid crystal compound changes whilecontinuously rotating in at least one in-plane direction, by adjusting apitch of a helical structure in the cholesteric liquid crystallinephase, a slope pitch of tilted surfaces of bright portions and darkportions with respect to a main surface in a case where a cross-sectionof the patterned cholesteric liquid crystal layer is observed with ascanning electron microscope (SEM) (an interval between bright portionsor between dark portions in the normal direction with respect to theslope is set as ½ surface pitch) can be adjusted, and the selectivereflection center wavelength with respect to oblique light can beadjusted.

In addition, the optical element according to the embodiment of thepresent invention includes a plurality of cholesteric liquid crystallayers. In a case where the optical element includes a plurality ofcholesteric liquid crystal layers, it is preferable that the opticalelement includes cholesteric liquid crystal layers having differenttwisted directions of helical structures. In addition, in a case wherethe optical element includes a plurality of cholesteric liquid crystallayers, at least one of the cholesteric liquid crystal layers may be apatterned cholesteric liquid crystal layer, and it is preferable thattwo or more of the cholesteric liquid crystal layers are patternedcholesteric liquid crystal layers.

In addition, in a case where the optical element according to theembodiment of the present invention includes two or more patternedcholesteric liquid crystal layers, it is preferable that the opticalelement includes patterned cholesteric liquid crystal layers havingdifferent twisted directions of helical structures.

For example, in FIG. 3 , in a patterned cholesteric liquid crystal layerthat has a liquid crystal alignment pattern in which a direction of anoptical axis derived from a liquid crystal compound rotates in onein-plane direction and that has regions having different pitches ofhelical structures in a plane, optically-anisotropic layers havingdifferent directions (senses of helical structures) of circularlypolarized light to be reflected may be laminated and used.

This way, the optical element further includes patterned cholestericliquid crystal layers having different directions (senses of helicalstructures) of circularly polarized light to be reflected such thatincidence light in various polarization states can be efficientlyreflected.

Here, it is preferable that the patterned cholesteric liquid crystallayers have the same (substantially the same) selective reflectioncenter wavelength.

This way, by providing the patterned cholesteric liquid crystal layershaving the same selective reflection center wavelength and differentdirections of circularly polarized light to be reflected, a reflectivityof specific light can be improved.

Here, in the patterned cholesteric liquid crystal layers having the sameselective reflection center wavelength and different directions ofcircularly polarized light to be reflected, it is preferable that therotation directions of the optical axes 30A of the liquid crystalcompound 30 in the liquid crystal alignment pattern are different fromeach other.

For example, in a case where the rotation direction of the optical axis30A of the liquid crystal compound 30 in the patterned cholestericliquid crystal layer 26 that reflects right circularly polarized lightof green light is clockwise as shown in FIG. 2 , it is preferable thatthe rotation direction of the optical axis 30A of the liquid crystalcompound 30 in the second patterned cholesteric liquid crystal layerthat reflects left circularly polarized light of green light iscounterclockwise.

In the patterned cholesteric liquid crystal layers in which the opticalaxis 30A of the liquid crystal compound 30 continuously rotates in thearrow X direction (the in-plane direction), in a case where thedirections of circularly polarized light are different from each otherand the rotation directions of the optical axes 30A are the same, areflection direction of circularly polarized light in the patternedcholesteric liquid crystal layer that reflects right circularlypolarized light is opposite to that in the patterned cholesteric liquidcrystal layer that reflects left circularly polarized light.

On the other hand, in the patterned cholesteric liquid crystal layershaving the same selective reflection center wavelength and differentdirections of circularly polarized light to be reflected, by setting therotation directions of the optical axes 30A of the liquid crystalcompound 30 in the liquid crystal alignment pattern to be opposite toeach other, a reflection direction (diffraction direction) of circularlypolarized light in the patterned cholesteric liquid crystal layer thatreflects right circularly polarized light can be made to be the same asthat in the patterned cholesteric liquid crystal layer that reflectsleft circularly polarized light.

In addition, this way, in a case where the optical element according tothe embodiment of the present invention includes the patternedcholesteric liquid crystal layers having the same selective reflectioncenter wavelength and different directions of circularly polarized lightto be reflected, it is preferable that the single periods A in theliquid crystal alignment patterns of the patterned cholesteric liquidcrystal layers having the same selective reflection center wavelengthare the same. As a result, a diffraction angle with respect to rightcircularly polarized light and a diffraction angle with respect to leftcircularly polarized light can be made to be the same.

However, the optical element according to the embodiment of the presentinvention is not limited to this configuration and may include acombination of patterned cholesteric liquid crystal layers havingdifferent directions of circularly polarized light to be reflected andincluding an overlapping portion in selective reflection wavelengthranges.

That is, in the optical element according to the embodiment of thepresent invention, even in a case where the selective reflectionwavelength ranges of the two patterned cholesteric liquid crystal layersforming the combination of the patterned cholesteric liquid crystallayers do not completely match each other, as long as at least a part ofthe selective reflection wavelength ranges includes an overlappingportion, light having a wavelength in the overlapping range (hatchedarea) can be reflected in a large amount of light.

Here, from the viewpoint of the amount of light reflected in the opticalelement, it is preferable that the patterned cholesteric liquid crystallayers forming the combination of the patterned cholesteric liquidcrystal layers include a wide overlapping range in the selectivereflection wavelength ranges. Specifically, in a case where a rangebetween two wavelengths of a half value transmittance of the patternedcholesteric liquid crystal layers forming the combination of thepatterned cholesteric liquid crystal layers is represented by Δλ_(h), adifference between selective reflection center wavelengths is preferably0.8 × Δλ_(h) nm or less, more preferably 0.6 × Δλ_(h) nm or less, andstill more preferably 0.4 × Δλ_(h) nm or less. In particular, it ispreferable that the selective reflection center wavelengths match eachother, and it is more preferable that the patterned cholesteric liquidcrystal layers have the same selective reflection wavelength range.

In a case where ranges between two wavelengths of a half valuetransmittance of the two patterned cholesteric liquid crystal layers aredifferent, the average value thereof is used as Δλ_(h).

In addition, in the optical element according to the embodiment of thepresent invention, it is preferable that the patterned cholestericliquid crystal layers forming the combination of the patternedcholesteric liquid crystal layers have the same single period A. In thepresent invention, the lengths of the single periods A in the liquidcrystal alignment patterns being the same represents that the differencebetween the lengths of the single periods A is 30% or lower.

Here, in the patterned cholesteric liquid crystal layers forming thecombination of the patterned cholesteric liquid crystal layers, it ispreferable that the difference between the lengths of the single periodsA in the liquid crystal alignment patterns is small. As described above,the length of the single period A decreases, the reflection angle withrespect to incidence light increases. Accordingly, as the differencebetween the lengths of the single periods A decreases, directions inwhich light is reflected from the patterned cholesteric liquid crystallayers forming the combination of the patterned cholesteric liquidcrystal layers can be made similar to each other. In the patternedcholesteric liquid crystal layers forming the combination of thepatterned cholesteric liquid crystal layers, the difference between thelengths of the single periods A in the liquid crystal alignment patternsis preferably 20% or lower and more preferably 10% or lower. It is stillmore preferable that the single periods A match each other.

In addition, in a case where the optical element according to theembodiment of the present invention includes two or more patternedcholesteric liquid crystal layers, it is also preferable that theoptical element includes patterned cholesteric liquid crystal layershaving the same twisted direction of helical structures.

For example, in FIG. 3 , in a patterned cholesteric liquid crystal layerthat has a liquid crystal alignment pattern in which a direction of anoptical axis derived from a liquid crystal compound rotates in onein-plane direction and that has regions having different pitches ofhelical structures in a plane, optically-anisotropic layers having thesame direction (sense of helical structures) of circularly polarizedlight to be reflected may be laminated and used.

Here, it is preferable that the patterned cholesteric liquid crystallayers have different selective reflection center wavelengths andinclude at least an overlapping portion in selective reflection centerwavelengths.

This way, in a case where the patterned cholesteric liquid crystallayers have different selective reflection center wavelengths, includeat least an overlapping portion in selective reflection centerwavelengths, and have the same direction of circularly polarized lightto be reflected, the selective reflection wavelength range can bewidened. By widening the selective reflection wavelength range,obliquely incident light can also be efficiently reflected. In a casewhere the optical element is used as a diffraction element of a lightguide element used in an AR display device or the like such as ARglasses, light can be efficiently reflected in a wide viewing anglerange.

Here, in the patterned cholesteric liquid crystal layers havingdifferent selective reflection center wavelengths and the same directionof circularly polarized light to be reflected, it is preferable that therotation directions of the optical axes 30A of the liquid crystalcompound 30 in the liquid crystal alignment pattern are the same as eachother.

In the patterned cholesteric liquid crystal layers having differentselective reflection center wavelengths and the same direction ofcircularly polarized light to be reflected, by setting the rotationdirections of the optical axes 30A of the liquid crystal compound 30 inthe liquid crystal alignment pattern to be the same as each other, areflection direction (diffraction direction) of circularly polarizedlight in the patterned cholesteric liquid crystal layer that reflectsright circularly polarized light can be made to be the same as that inanother patterned cholesteric liquid crystal layer that reflects rightcircularly polarized light.

In addition, this way, in a case where the optical element according tothe embodiment of the present invention includes the patternedcholesteric liquid crystal layers having different selective reflectioncenter wavelengths and the same direction of circularly polarized lightto be reflected, it is preferable that the single periods A in theliquid crystal alignment patterns of the patterned cholesteric liquidcrystal layers having the same selective reflection center wavelengthare the same. As a result, a diffraction angle with respect to rightcircularly polarized light and a diffraction angle with respect tocircularly polarized light of another layer can be made to be the same.

In addition, the optical element according to the embodiment of thepresent invention may include a plurality of patterned cholestericliquid crystal layers having different selective reflection centerwavelengths corresponding to color images. In a case where the opticalelement includes a plurality of patterned cholesteric liquid crystallayers having different selective reflection center wavelengths, it ispreferable that a permutation of the lengths of the selective reflectioncenter wavelengths and a permutation of the lengths of the singleperiods A in the liquid crystal alignment patterns of the patternedcholesteric liquid crystal layers are the same as each other.

Here, a reflection angle of light from the patterned cholesteric liquidcrystal layer in which the optical axis 30A of the liquid crystalcompound 30 continuously rotates in the in-plane direction (arrow Xdirection) varies depending on wavelengths of light to be reflected.Specifically, as the wavelength of light increases, the angle ofreflected light with respect to incidence light increases. Accordingly,in a case where red light, green light, and blue light are reflected,the reflection angles of red light, green light, and blue light aredifferent from each other. Specifically, in a case where cholestericreflecting layers having the same pitch A of the liquid crystalalignment pattern and having reflection center wavelengths of red,green, blue light are compared to each other, regarding the angle ofreflected light with respect to incidence light, the angle of red lightis the largest, the angle of green light is the second largest, and theangle of blue light is the smallest. Therefore, for example, in a lightguide plate of AR glasses, in a case where a reflection element that isformed of cholesteric liquid crystal layers having the same pitch A ofthe liquid crystal alignment pattern and different reflection centerwavelengths is used as a diffraction element for incidence and emissionof light into and from the light guide plate, in the case of a fullcolor image, reflection directions of red light, green light, and bluelight are different from each other, and incidence angle ranges in whichred light, green light, and blue light are totally reflected from thelight guide plate are different from each other. Therefore, a visualfield range in which red light, green light, and blue light can be seenat the same time is narrowed.

In addition, a reflection angle of light from the patterned cholestericliquid crystal layer in which the optical axis 30A of the liquid crystalcompound 30 continuously rotates in the arrow X direction (in-planedirection) varies depending on the length A of the single period of theliquid crystal alignment pattern over which the optical axis 30A rotatesby 180° in the arrow X direction, that is, depending on the singleperiod A. Specifically, as the length of the single period A decreases,the angle of reflected light with respect to incidence light increases.

Accordingly, a permutation of the lengths of the selective reflectioncenter wavelengths in the patterned cholesteric liquid crystal layersand a permutation of the lengths of the single periods A in the liquidcrystal alignment patterns are the same as each other such that thewavelength dependence on the reflection angle of light to be reflectedfrom the patterned cholesteric liquid crystal layer is significantlyreduced, and light components having different wavelengths can bereflected substantially in the same direction.

As a result, even in a case where a full color image is displayed by redlight, green light, and blue light, the light can be guided to the lightguide plate without a deviation in reflection angle at each wavelength,and a full color image can be displayed with a wide visual field.

Method of Forming Regions Having Different Helical Pitches

In the configuration in which the patterned cholesteric liquid crystallayer has regions having different helical pitches, the chiral agent inwhich back isomerization, dimerization, isomerization, dimerization orthe like occurs during light irradiation such that the helical twistingpower (HTP) changes is used. By irradiating the liquid crystalcomposition with light having a wavelength at which the HTP of thechiral agent changes before or during the curing of the liquid crystalcomposition for forming the patterned cholesteric liquid crystal layerwhile changing the irradiation dose for each of the regions, the regionshaving different helical pitches can be formed.

For example, by using a chiral agent in which the HTP decreases duringlight irradiation, the HTP of the chiral agent decreases during lightirradiation. Here, by changing the irradiation dose of light for each ofthe regions, for example, in a region that is irradiated with the lightat a high irradiation dose, the decrease in HTP is large, the inductionof helix is small, and thus the helical pitch increases. On the otherhand, for example, in a region that is irradiated with the light at alow irradiation dose, the decrease in HTP is small, helix is induced bythe original HTP of the chiral agent, and thus the helical pitchdecreases.

The method of changing the irradiation dose of light for each of theregions is not particularly limited, and a method of irradiating lightthrough a gradation mask, a method of changing the irradiation time foreach of the regions, or a method of changing the irradiation intensityfor each of the regions can be used.

The gradation mask refers to a mask in which a transmittance withrespect to light for irradiation changes in a plane.

Light Guide Element and Image Display Device

A light guide element according to the embodiment of the presentinvention includes the above-described optical element and a light guideplate.

An image display device according to the embodiment of the presentinvention is suitably used as an AR display device such as augmentedreality (AR) glasses, and includes a light guide element and a displayelement.

FIG. 6 conceptually shows an example of the image display device (ARdisplay device) according to the embodiment of the present invention.

An AR display device 50 shown in FIG. 6 includes a display (displayelement) 40 and a light guide element 45.

The light guide element 45 is the light guide element according to theembodiment of the present invention and includes the optical element 10according to the embodiment of the present invention, a light guideplate 44, and a diffraction element 42.

The light guide plate 44 guides light in a rectangular shape that iselongated in one direction.

As shown in FIG. 6 , the diffraction element 42 is disposed on a surface(main surface) of the light guide plate 44 on one end portion side in alongitudinal direction. In addition, the optical element 10 is disposedon a surface of the light guide plate 44 on another end portion side.The disposition position of the diffraction element 42 corresponds to alight incidence position of the light guide plate 44, and thedisposition position of the optical element 10 corresponds to a lightemission position of the light guide plate 44. In addition, thediffraction element 42 and the optical element 10 are disposed on thesame surface of the light guide plate 44.

The light guide plate 44 is not particularly limited, and a well-knownlight guide plate of the related art that is used in an image displaydevice or the like can be used.

The diffraction element 42 diffracts light emitted from the display 40and incident into the light guide plate 44 such that the light istotally reflected in the light guide plate 44.

The diffraction element 42 is not particularly limited, and variousdiffraction elements used in an AR display device, for example, a relieftype diffraction element, a diffraction element using liquid crystal, ora volume hologram element can be used.

In addition, the diffraction element 42 is not limited to a reflectiontype diffraction element and may be a transmission type diffractionelement. In a case where the diffraction element 42 is a transmissiontype diffraction element, the diffraction element 42 is disposed on asurface of the light guide plate 44 facing the display 40.

As shown in FIG. 6 , the display 40 is disposed on a surface of one endportion of the light guide plate 44 opposite to the surface where thediffraction element 42 is disposed. In addition, a surface of the oneend portion of the light guide plate 44 opposite to the surface wherethe optical element 10 is disposed is an observation position of a userU.

In the following description, the longitudinal direction of the lightguide plate 44 will be referred to as “X direction”, and a directionthat is perpendicular to the X direction and perpendicular to thesurface of the optical element 10 will be referred to as “Z direction”.The Z direction may be a laminating direction of the respective layersof the optical element 10.

The display 40 is not particularly limited. For example, variouswell-known displays used in an AR display device such as AR glasses canbe used.

Examples of the display 40 include devices employing a liquid crystaldisplay (LCOS including Liquid Crystal On Silicon), an organicelectroluminescence display, digital light processing (DLP), or MicroElectro Mechanical Systems (MEMS).

The display 40 may display a monochrome image, a two-color image, or acolor image.

In addition, light emitted from the display 40 may be unpolarized lightor polarized light and is preferably circularly polarized light. In acase where the display 40 emits circularly polarized light, the lightguide element 45 can efficiently guide the light emitted from thedisplay 40.

In the AR display device 50 having the above-described configuration, asindicated by arrows, light displayed by the display 40 is incident intothe light guide plate 44 from the surface of the one end portion of thelight guide plate 44 opposite to the surface where the diffractionelement 42 is disposed. The light incident into the light guide plate 44is reflected from an interface between the light guide plate 44 and thediffraction element 42. At this time, the light is reflected in adirection having an angle different from that of a specular reflectiondirection due to the diffraction effect of the diffraction element 42without being specularly reflected (regularly reflected). In the exampleshown in FIG. 6 , light is incident from a direction (Z direction)substantially perpendicular to the diffraction element 42, and isreflected in a direction that is tilted with a large angle from theperpendicular direction toward the longitudinal direction (X direction)of the light guide plate 44.

Since the light reflected from the diffraction element 42 is reflectedwith a large angle with respect to the angle of the incidence light, anangle of a light traveling direction with respect to the surface of thelight guide plate 44 is small. Therefore, the light is totally reflectedfrom the both surfaces (interface) of the light guide plate 44 and isguided in the longitudinal direction (X direction) in the light guideplate 44.

The light guided in the light guide plate 44 is reflected from theinterface between the light guide plate 44 and the optical element 10 inanother end portion of the light guide plate 44 in the longitudinaldirection. At this time, the light is reflected in a direction having anangle different from that of a specular reflection direction due to thediffraction effect of the optical element 10 without being specularlyreflected. In the example shown in FIG. 6 , the light is incident froman oblique direction with respect to the optical element 10 and isreflected in a direction perpendicular to the surface of the opticalelement 10.

The light reflected from the optical element 10 reaches the surface ofthe light guide plate 44 opposite to the surface where the opticalelement 10 is disposed, but is incident to be substantiallyperpendicular to the surface. Therefore, the light is emitted to theoutside of the light guide plate 44 without being totally reflected.That is, the light is emitted to the observation position of the user U.

This way, in an AR display device 50, an image displayed by the display40 is incident into one end of the light guide plate 44, propagates inthe light guide plate 44, and is emitted from another end of the lightguide plate 44 such that the virtual image is displayed to besuperimposed on a scene that is actually being seen by the user U.

Here, in the light guide element 45, the diffraction efficiency of thepatterned cholesteric liquid crystal layer of the optical element 10 isadjusted, and in a case where the light propagated in the light guideplate 44 is diffracted by the optical element 10, a part of the light isdiffracted at a plurality of positions to be emitted to the outside ofthe light guide plate 44. As a result, the viewing zone can be expanded(exit pupil expansion).

Specifically, in FIG. 6 , light I₀ propagated in the light guide plate44 reaches the position of the optical element 10 while being repeatedlyreflected from both surfaces (interface) of the light guide plate 44. Apart of the light I₀ at the position of the optical element 10 isdiffracted in a region (position) P₁ close to the incidence side to beemitted from the light guide plate 44 (emitted light R₁). In addition,light I₁ that is not diffracted further propagates in the light guideplate 44, and partial light R₂ is diffracted at a position P₂ of theoptical element 10 to emitted from the light guide plate 44. Light I₂that is not diffracted further propagates in the light guide plate 44,and partial light R₃ is diffracted at a position P₃ of the opticalelement 10 to emitted from the light guide plate 44. In addition, lightI₃ that is not diffracted further propagates in the light guide plate44, and partial light R₄ is diffracted at a position P₄ of the opticalelement 10 to emitted from the light guide plate 44.

This way, with the configuration where the light propagated in the lightguide plate 44 is diffracted by the optical element 10 at a plurality ofpositions to be emitted to the outside of the light guide plate 44, theviewing zone can be expanded (exit pupil expansion).

Here, a case where the diffraction efficiency of the optical element 10is constant in a plane is assumed. In a case where the diffractionefficiency is constant, the light intensity (light amount) of theincident light I0 is high in the region (position) P₁ close to theincidence side. Therefore, the intensity of the emitted light R₁ is alsohigh. Next, the light I₁ that is not diffracted propagates in the lightguide plate 44 and is diffracted again at the position P₂ of the opticalelement 10 such that the partial light R₂ is emitted. However, theintensity of the light I₁ is lower than that of the light I₀. Therefore,even in a case where the light components are diffracted with the samediffraction efficiency, the intensity of the light R₂ is lower than thatof the light R₁ reflected from the region close to the incidence side.Likewise, the light I₂ that is not diffracted propagates in the lightguide plate 44 and is diffracted again at the position P₃ of the opticalelement 10 such that the partial light R₃ is emitted. However, theintensity of the light I₂ is lower than that of the light I₁. Therefore,even in a case where the light components are diffracted with the samediffraction efficiency, the intensity of the light R₃ is lower than thatof the light R₂ reflected from the position P₂. Further, the intensityof the light R₄ reflected from the region P₄ distant from the incidenceside is lower than the light R₃.

This way, in a case where the diffraction efficiency of the opticalelement 10 is constant, light having a high light intensity is emittedfrom the region close to the incidence side, and light having a lowlight intensity is emitted from the region distant from the incidenceside. Therefore, there is a problem in that, as indicated by a brokenline in FIG. 7 , the intensity of emitted light is not uniform dependingon positions.

On the other hand, the optical element 10 according to the embodiment ofthe present invention has the configuration in which the patternedcholesteric liquid crystal layer has regions having different pitches ofhelical structures in a plane, and the helical pitch gradually changesfrom one side toward another side in the in-plane direction in which theoptical axis rotates.

As a result, the optical element 10 can be configured such that thediffraction efficiency of the patterned cholesteric liquid crystal layerincreases from one side toward another side in the in-plane direction inwhich the optical axis rotates (refer to FIG. 5 ), and the opticalelement 10 can be disposed in the light guide element 45 such that thediffraction efficiency of an optically-anisotropic layer 18 increases inthe light traveling direction in the light guide plate 44. That is, inthe example shown in FIG. 6 , the patterned cholesteric liquid crystallayer of the optical element 10 can be configured such that thediffraction efficiency increases from the left toward the right in FIG.6 .

In this case, at the position P₁ close to the incidence side, theintensity (light amount) of the incident light I₀ is high, but thediffraction efficiency is low. Therefore, the intensity of the emittedlight R₁ is high to some extent. Next, the light I₁ that is notdiffracted propagates in the light guide plate 44 and is diffractedagain at the position P₂ of the optical element 10 such that the partiallight R₂ is emitted. At this time, the intensity of the light I₁ islower than that of the light I₀, but the diffraction efficiency at theposition P₂ is higher than that at the position P₁. Therefore, theintensity of the light R₂ can be made to be the same as that of thelight R₁ reflected from the position P₁. Likewise, the light I₂ that isnot diffracted propagates in the light guide plate 44 and is diffractedagain at the position P₃ of the optical element 10 such that the partiallight R₃ is emitted. At this time, the intensity of the light I₂ islower than that of the light I₁, but the diffraction efficiency at theposition P₃ is higher than that at the position P₂. Therefore, theintensity of the light R₃ can be made to be the same as that of thelight R₂ reflected from the position P₂. Further, the diffractionefficiency at the region P₄ distant from the incidence side is higherthan that at the position P₃. Therefore, the intensity of the light R₄can be made to be the same as that of the light R₃ reflected from theposition P₃.

This way, the diffraction efficiency of the optical element 10 isconfigured to increase from one side toward another side in the in-planedirection in which the optical axis rotates. As a result, light having aconstant light intensity can be emitted from any position of the opticalelement 10. Therefore, as indicated by a solid line in FIG. 7 , theintensity of emitted light can be made uniform irrespective ofpositions.

In FIG. 6 , light is indicated by an arrow, the light emitted from thedisplay 40 may be a surface shape. The surface-shaped light propagatesin the light guide plate 44 while maintaining a positional relationship,and is diffracted by the optical element 10.

A distribution of the diffraction efficiency of the patternedcholesteric liquid crystal layer may be appropriately set based on thelength of the patterned cholesteric liquid crystal layer, the thicknessof the light guide plate, the wavelength of light, and the like suchthat the intensity of emitted light can be made to be uniform.

In addition, the diffraction efficiency of the patterned cholestericliquid crystal layer is preferably 0.5% to 20% and more preferably 1% to10% in a region having a low diffraction efficiency, and is preferably20% to 100% and more preferably 30% to 95% in a region having a highdiffraction efficiency.

In addition, the helical pitch of the patterned cholesteric liquidcrystal layer may be set according to the distribution of thediffraction efficiency.

In addition, in the description of FIG. 6 , the optical element 10includes one patterned cholesteric liquid crystal layer. The opticalelement 10 may include a plurality of patterned cholesteric liquidcrystal layers. Alternatively, in the light guide element 45, aplurality of optical elements 10 including the single patternedcholesteric liquid crystal layer may be laminated.

In a case where the optical element 10 includes a plurality of patternedcholesteric liquid crystal layers, or in a case where the light guideelement 45 includes a plurality of optical elements 10, that is,includes a plurality of patterned cholesteric liquid crystal layers, itis preferable that the light guide element 45 includes a plurality ofpatterned cholesteric liquid crystal layers having different selectivereflection wavelengths. For example, the optical element may includepatterned cholesteric liquid crystal layers having selective reflectionwavelengths of red light, green light, and blue light. As a result, theoptical element (the laminate thereof) can diffract red light, greenlight, and blue light, respectively, and the light guide element 45 canappropriately guide light of the display 40 that displays a color image.

Alternatively, the optical element may include two patterned cholestericliquid crystal layers having the same selective reflection wavelengththat reflect circularly polarized light components having oppositeturning directions. For example, the optical element may include apatterned cholesteric liquid crystal layer that reflects rightcircularly polarized light of red light and a patterned cholestericliquid crystal layer that reflects left circularly polarized light ofred light. As a result, the optical element (the laminate thereof) candiffract right circularly polarized light and left circularly polarizedlight, respectively, and The light guide element 45 can guide rightcircularly polarized light and left circularly polarized light, and thusthe light use efficiency can be improved.

In addition, in the example shown in FIG. 6 , the light guide element 45includes the diffraction element on each of the incidence side and theemission side. However, the present invention is not limited thereto,and an intermediate diffraction element may be provided.

FIG. 8 is a front view schematically showing another example of thelight guide element according to the embodiment of the presentinvention, and FIG. 9 is a top view of FIG. 8 .

A light guide element 110 shown in FIGS. 8 and 9 includes a light guideplate 112, a first diffraction element 114, a second diffraction element116, and a third diffraction element 118.

The first diffraction element 114 diffracts light incident from theoutside at an angle at which the light can be totally reflected in thelight guide plate 112.

The second diffraction element 116 diffracts light that is incident intothe light guide plate 112 at a position of the first diffraction element114 and propagated in the light guide plate 112 such that a lighttraveling direction in the light guide plate 112 is bent.

The third diffraction element 118 diffracts light that is diffracted bythe second diffraction element 116 and propagated in the light guideplate 112 at an angle where the light can be emitted from the lightguide plate 112 to the outside.

That is, in the light guide element 110 shown in FIGS. 8 and 9 , lightthat is diffracted in the first diffraction element 114 for incidenceand incident into the light guide plate 112 is diffracted by theintermediate second diffraction element 116 such that a light travelingdirection is bent in the light guide plate 112, and then is diffractedby the third diffraction element 118 on the emission side to be emittedto the outside of the light guide plate 112.

In this configuration, exit pupil expansion can be performed in thesecond diffraction element 116 and/or the third diffraction element. Atthis time, by using the optical element according to the embodiment ofthe present invention as the second diffraction element 116 and/or thethird diffraction element 118, the amount of light expanded can be madeto be uniform. From the viewpoint that the light amount can be made tobe more uniform, it is preferable that the optical element according tothe embodiment of the present invention is used as the seconddiffraction element 116 and the third diffraction element 118.

In this case, the optical element according to the embodiment of thepresent invention may be included as the second diffraction element 116and/or the third diffraction element, and various well-known diffractionelements of the related art such as a relief type diffraction element, adiffraction element using liquid crystal, or a volume hologram elementcan be used as other diffraction elements.

In addition, it is preferable that each of the first diffraction element114, the second diffraction element 116, and the third diffractionelement 118 is an optical element including a patterned cholestericliquid crystal layer that is obtained by immobilizing a cholestericliquid crystalline phase, in which the patterned cholesteric liquidcrystal layer has a liquid crystal alignment pattern in which adirection of an optical axis derived from a liquid crystal compoundchanges while continuously rotating in at least one in-plane direction.

At this time, it is preferable that, in a case where lengths of singleperiods of the liquid crystal alignment patterns in the firstdiffraction element, the second diffraction element, and the thirddiffraction element are represented by Λ₁, Λ₂, and Λ₃, respectively,Λ₂<Λ₁, and Λ₂< Λ₃ are satisfied.

In a case where the lengths of the single periods of the liquid crystalalignment patterns of the first diffraction element, the seconddiffraction element, and the third diffraction element satisfy Λ₂<Λ₁,and Λ₂<Λ₃,light can be suitably propagated from the first diffractionelement to the third diffraction element, and light can be appropriatelyemitted from the light guide plate to the user U.

In all the above-described optical elements according to the embodimentof the present invention, the optical axis 30A of the liquid crystalcompound 30 in the liquid crystal alignment pattern of the cholestericliquid crystal layer continuously rotates only in the arrow X direction.

However, the present invention is not limited thereto, and variousconfigurations can be used as long as the optical axis 30A of the liquidcrystal compound 30 in the cholesteric liquid crystal layer continuouslyrotates in the in-plane direction.

The optical element according to the embodiment of the present inventioncan be used for various uses where light is reflected at an angle otherthan the angle of specular reflection, for example, an optical pathchanging member, a light gathering element, a light diffusing element toa predetermined direction, a diffraction element, or the like in anoptical device.

In the above-described example, the optical element according to theembodiment of the present invention is used as the optical element thatreflects visible light. However, the present invention is not limited tothis example, and various configurations can be used.

For example, the optical element according to the embodiment of thepresent invention also may be configured to reflect infrared light orultraviolet light or to reflect only light other than visible light.

Hereinabove, the optical element according to the first aspect of thepresent invention has been described above. However, the presentinvention is not limited to the above-described examples, and variousimprovements and modifications can be made within a range not departingfrom the scope of the present invention.

Second Aspect

Hereinafter, an optical element and a light guide element according to asecond aspect of the present invention will be described in detail basedon preferable embodiments shown in the accompanying drawings.

In the present specification, numerical ranges represented by “to”include numerical values before and after “to” as lower limit values andupper limit values.

In the present specification, “(meth)acrylate” represents “either orboth of acrylate and methacrylate”.

In the present specification, the meaning of “the same” includes a casewhere an error range is generally allowable in the technical field. Inaddition, in the present specification, the meaning of “all”, “entire”,or “entire surface” includes not only 100% but also a case where anerror range is generally allowable in the technical field, for example,99% or more, 95% or more, or 90% or more.

In the present specification, visible light refers to light which can beobserved by human eyes among electromagnetic waves and refers to lightin a wavelength range of 380 to 780 nm. Invisible light refers to lightin a wavelength range of shorter than 380 nm or longer than 780 nm.

In addition, although not limited thereto, in visible light, light in awavelength range of 420 to 490 nm refers to blue light, light in awavelength range of 495 to 570 nm refers to green light, and light in awavelength range of 620 to 750 nm refers to red light.

In the present specification, a selective reflection center wavelengthrefers to an average value of two wavelengths at which, in a case wherea minimum value of a transmittance of a target object (member) isrepresented by Tmin (%), a half value transmittance: T½ (%) representedby the following expression is exhibited.

-   Expression for obtaining Half Value Transmittance: T½ = 100 - (100 -    Tmin) ÷ 2

In addition, selective reflection center wavelengths of a plurality oflayers being “equal” does not represent that the selective reflectioncenter wavelengths are exactly equal, and error is allowed in a rangewhere there are no optical effects. Specifically, selective reflectioncenter wavelengths of a plurality of objects being “equal” represents adifference between the selective reflection center wavelengths of therespective objects is 20 nm or less, and this difference is preferably15 nm or less and more preferably 10 nm or less.

In the present specification, Re(λ) represents an in-plane retardationat a wavelength λ. Unless specified otherwise, the wavelength λ refersto 550 nm.

In the present specification, Re(λ) is a value measured at thewavelength λ using AxoScan (manufactured by Axometrics, Inc.). Byinputting an average refractive index ((nx+ny+nz)/3) and a thickness (d(µm)) to AxoScan, the following expressions can be calculated.

-   Slow Axis Direction (°)-   Re(λ) = R0(λ)-   R0(λ) is expressed as a numerical value calculated by AxoScan and    represents Re(λ).

The optical element according to the embodiment of the present inventionis a light reflection element that reflects incident light and includesa patterned cholesteric liquid crystal layer obtained by immobilizing acholesteric liquid crystalline phase.

In the optical element according to the embodiment of the presentinvention, the patterned cholesteric liquid crystal layer has a liquidcrystal alignment pattern in which a direction of an optical axisderived from a liquid crystal compound changes while continuouslyrotating in at least one in-plane direction. Here, in the liquid crystalalignment pattern, a length over which the direction of the optical axisrotates by 180° in the in-plane direction in which the direction of theoptical axis changes while continuously rotating is set as a singleperiod. In addition, the patterned cholesteric liquid crystal layer hasregions having different pitches of helical structures in a plane.Further, in a case where a length over which the direction of theoptical axis derived from the liquid crystal compound rotates by 180° ina plane is set as a single period, the cholesteric liquid crystal layerhas regions having different lengths of the single periods.

Although described in detail below, with the optical element accordingto the embodiment of the present invention having the above-describedstructure, the reflection angle dependence of the amount of lightreflected in a plane is small, and in a case where light incident intodifferent regions in a plane is reflected at different angles, thebrightness of the reflected light can be increased.

First Embodiment

FIG. 12 is a diagram conceptually showing an example of the opticalelement according to the embodiment of the present invention.

An optical element 10 shown in the drawing selectively reflects lighthaving a specific wavelength and includes a first reflecting layer 14.

In the optical element 10, the first reflecting layer 14 includes asupport 20, an alignment film 24, and a patterned cholesteric liquidcrystal layer 26.

In addition, the optical element 10 shown in the drawing includes thesupport 20 for the reflecting layer. However, the optical elementaccording to the embodiment of the present invention does notnecessarily include the support 20 for the reflecting layer.

For example, the optical element according to the embodiment of thepresent invention may be formed of only the alignment film and thecholesteric liquid crystal layer or may be formed of only thecholesteric liquid crystal layer by peeling off the support 20 of thefirst reflecting layer 14 from the above-described configuration.

That is, the optical element according to the embodiment of the presentinvention can use various layer configurations as long as the patternedcholesteric liquid crystal layer has a liquid crystal alignment patternin which a direction of an optical axis derived from a liquid crystalcompound changes while continuously rotating in at least one in-planedirection, the cholesteric liquid crystal layer has regions havingdifferent pitches of helical structures in a plane, and in a case wherea length over which the direction of the optical axis derived from theliquid crystal compound rotates by 180° in a plane is set as a singleperiod, the patterned cholesteric liquid crystal layer has regionshaving different lengths of the single periods.

The above-described point can be applied to all the optical elementsaccording to respective aspects of the present invention describedbelow.

Support

In the first reflecting layer 14, the support 20 supports the alignmentfilm 24 and the patterned cholesteric liquid crystal layer 26.

As the support 20, various sheet-shaped materials (films or plate-shapedmaterials) can be used as long as they can support the alignment film 24and the patterned cholesteric liquid crystal layer 26.

A transmittance of the support 20 with respect to corresponding light ispreferably 50% or higher, more preferably 70% or higher, and still morepreferably 85% or higher.

The thickness of the support 20 is not particularly limited and may beappropriately set depending on the use of the optical element 10, amaterial for forming the support 20, and the like in a range where thealignment film 24 and the patterned cholesteric liquid crystal layer 26can be supported.

The thickness of the support 20 is preferably 1 to 1000 µm, morepreferably 3 to 250 µm, and still more preferably 5 to 150 µm.

The support 20 may have a single-layer structure or a multi-layerstructure.

In a case where the support 20 has a single-layer structure, examplesthereof include supports formed of glass, triacetyl cellulose (TAC),polyethylene terephthalate (PET), polycarbonates, polyvinyl chloride,acryl, polyolefin, and the like. In a case where the support 20 has amulti-layer structure, examples thereof include a support including: oneof the above-described supports having a single-layer structure that isprovided as a substrate; and another layer that is provided on a surfaceof the substrate.

Alignment Film

In the first reflecting layer 14, the alignment film 24 is formed on asurface of the support 20. The alignment film 24 is an alignment filmfor aligning the liquid crystal compound 30 to a predetermined liquidcrystal alignment pattern during the formation of the patternedcholesteric liquid crystal layer 26 of the first reflecting layer 14.

The following description regarding the alignment film is alsoapplicable to an alignment film provided in the reflection memberdescribed below. Accordingly, in the following description, in a casewhere it is not necessary to distinguish the alignment film from anotheralignment film, the alignment films will also be simply referred to as“alignment film”. In addition, in a case where it is not necessary todistinguish the reflecting layer 14 and the patterned cholesteric liquidcrystal layer 26 from another cholesteric liquid crystal layer, thereflecting layer 14 and the patterned cholesteric liquid crystal layer26 will also be simply referred to as “cholesteric liquid crystallayer”.

Although described below, in the optical element 10 according to theembodiment of the present invention, the patterned cholesteric liquidcrystal layer has a liquid crystal alignment pattern in which adirection of an optical axis 30A (refer to FIG. 14 ) derived from theliquid crystal compound 30 changes while continuously rotating in onein-plane direction.

In addition, in the liquid crystal alignment pattern, a length overwhich the direction of the optical axis 30A rotates by 180° in thein-plane direction in which the direction of the optical axis 30Achanges while continuously rotating is set as a single period A (arotation period of the optical axis).

In the following description, “the direction of the optical axis 30Arotates” will also be simply referred to as “the optical axis 30Arotates”.

As the alignment film, various well-known films can be used.

Examples of the alignment film include a rubbed film formed of anorganic compound such as a polymer, an obliquely deposited film formedof an inorganic compound, a film having a microgroove, and a film formedby lamination of Langmuir-Blodgett (LB) films formed with aLangmuir-Blodgett’s method using an organic compound such asω-tricosanoic acid, dioctadecylmethylammonium chloride, or methylstearate.

The alignment film formed by a rubbing treatment can be formed byrubbing a surface of a polymer layer with paper or fabric in a givendirection multiple times.

As the material used for the alignment film, for example, a material forforming polyimide, polyvinyl alcohol, a polymer having a polymerizablegroup described in JP1997-152509A (JP-H9-152509A), or an alignment filmsuch as JP2005-097377A, JP2005-099228A, and JP2005-128503A ispreferable.

In the optical element 10 according to the embodiment of the presentinvention, for example, the alignment film can be suitably used as aso-called photo-alignment film obtained by irradiating a photo-alignablematerial with polarized light or non-polarized light. That is, in theoptical element 10 according to the embodiment of the present invention,a photo-alignment film that is formed by applying a photo-alignablematerial to the support 20 is suitably used as the alignment film.

The irradiation of polarized light can be performed in a directionperpendicular or oblique to the photo-alignment film, and theirradiation of non-polarized light can be performed in a directionoblique to the photo-alignment film.

Preferable examples of the photo-alignable material used in thephoto-alignment film that can be used in the present invention include:an azo compound described in JP2006-285197A, JP2007-076839A,JP2007-138138A, JP2007-094071A, JP2007-121721A, JP2007-140465A,JP2007-156439A, JP2007-133184A, JP2009-109831A, JP3883848B, andJP4151746B; an aromatic ester compound described in JP2002-229039A; amaleimide- and/or alkenyl-substituted nadiimide compound having aphoto-alignable unit described in JP2002-265541A and JP2002-317013A; aphotocrosslinking silane derivative described in JP4205195B andJP4205198B, a photocrosslinking polyimide, a photocrosslinkingpolyamide, or a photocrosslinking polyester described in JP2003-520878A,JP2004-529220A, and JP4162850B; and a photodimerizable compound, inparticular, a cinnamate compound, a chalcone compound, or a coumarincompound described in JP1997-118717A (JP-H9-118717A), JP1998-506420A(JP-H10-506420A), JP2003-505561A, WO2010/150748A, JP2013-177561A, andJP2014-012823A.

Among these, an azo compound, a photocrosslinking polyimide, aphotocrosslinking polyamide, a photocrosslinking polyester, a cinnamatecompound, or a chalcone compound is suitability used.

The thickness of the alignment film is not particularly limited. Thethickness with which a required alignment function can be obtained maybe appropriately set depending on the material for forming the alignmentfilm.

The thickness of the alignment film is preferably 0.01 to 5 µm and morepreferably 0.05 to 2 µm.

A method of forming the alignment film is not limited. Any one ofvarious well-known methods corresponding to a material for forming thealignment film can be used. For example, a method including: applyingthe alignment film to a surface of the support 20; drying the appliedalignment film; and exposing the alignment film to laser light to forman alignment pattern can be used.

FIG. 16 conceptually shows an example of an exposure device that exposesthe alignment film to form an alignment pattern. In the example shown inFIG. 16 , for example, the exposure of the alignment film 24 of thefirst reflecting layer 14 is shown.

An exposure device 60 shown in FIG. 16 includes: a light source 64including a laser 62; an λ/2 plate 65 that changes a polarizationdirection of laser light M emitted from the laser 62; a polarizationbeam splitter 68 that splits the laser light M emitted from the laser 62into two beams MA and MB; mirrors 70A and 70B that are disposed onoptical paths of the splitted two beams MA and MB; and λ/4 plates 72Aand 72B.

Although not shown in the drawing, the light source 64 emits linearlypolarized light P₀. The λ/4 plate 72A converts the linearly polarizedlight P₀ (beam MA) into right circularly polarized light P_(R), and theλ/4 plate 72B converts the linearly polarized light P₀ (beam MB) intoleft circularly polarized light P_(L).

The support 20 including the alignment film 24 on which the alignmentpattern is not yet formed is disposed at an exposed portion, the twobeams MA and MB intersect and interfere each other on the alignment film24, and the alignment film 24 is irradiated with and exposed to theinterference light.

Due to the interference at this time, the polarization state of lightwith which the alignment film 24 is irradiated periodically changesaccording to interference fringes. As a result, in the alignment film24, an alignment pattern in which the alignment state periodicallychanges can be obtained. That is, an alignment film (hereinafter, alsoreferred to as “patterned alignment film”) having an alignment patternin which the alignment state changes periodically is obtained.

In the exposure device 60, by changing an intersection angle α betweenthe two beams MA and MB, the period of the alignment pattern can beadjusted. That is, by adjusting the intersection angle α in the exposuredevice 60, in the alignment pattern in which the optical axis 30Aderived from the liquid crystal compound 30 continuously rotates in thein-plane direction, the length of the single period over which theoptical axis 30A rotates by 180° in the in-plane direction in which theoptical axis 30A rotates can be adjusted.

By forming the cholesteric liquid crystal layer on the patternedalignment film having the alignment pattern in which the alignment stateperiodically changes, as described below, the patterned cholestericliquid crystal layer 26 having the liquid crystal alignment pattern inwhich the optical axis 30A derived from the liquid crystal compound 30continuously rotates in the in-plane direction can be formed.

In addition, by rotating the optical axes of the λ/4 plates 72A and 72Bby 90°, respectively, the rotation direction of the optical axis 30A canbe reversed.

As described above, the patterned alignment film has a liquid crystalalignment pattern in which the liquid crystal compound is aligned suchthat the direction of the optical axis of the liquid crystal compound inthe patterned cholesteric liquid crystal layer formed on the patternedalignment film changes while continuously rotating in at least onein-plane direction. In a case where an axis in the direction in whichthe liquid crystal compound is aligned is an alignment axis, it can besaid that the patterned alignment film has an alignment pattern in whichthe direction of the alignment axis changes while continuously rotatingin at least one in-plane direction. The alignment axis of the patternedalignment film can be detected by measuring absorption anisotropy. Forexample, in a case where the amount of light transmitted through thepatterned alignment film is measured by irradiating the patternedalignment film with linearly polarized light while rotating thepatterned alignment film, it is observed that a direction in which thelight amount is the maximum or the minimum gradually changes in thein-plane direction.

In the optical element according to the embodiment of the presentinvention, the alignment film is provided as a preferable aspect and isnot an essential component.

For example, the following configuration can also be adopted, in which,by forming the alignment pattern on the support 20 using a method ofrubbing the support 20, a method of processing the support 20 with laserlight or the like, or the like, the patterned cholesteric liquid crystallayer has the liquid crystal alignment pattern in which the direction ofthe optical axis 30A derived from the liquid crystal compound 30 changeswhile continuously rotating in at least one in-plane direction.

Patterned Cholesteric Liquid Crystal Layer

In the first reflecting layer 14, the patterned cholesteric liquidcrystal layer 26 is formed on the surface of the alignment film 24.

In FIG. 14 , in order to simplify the drawing and to clarify theconfiguration of the optical element 10, only the liquid crystalcompound 30 (liquid crystal compound molecules) on the surface of thealignment film in the patterned cholesteric liquid crystal layer 26 isconceptually shown. However, as conceptually shown in FIG. 13 , thepatterned cholesteric liquid crystal layer 26 has a helical structure inwhich the liquid crystal compound 30 is helically turned and laminatedas in a cholesteric liquid crystal layer obtained by immobilizing atypical cholesteric liquid crystalline phase. In the helical structure,a configuration in which the liquid crystal compound 30 is helicallyrotated once (rotated by 360) and laminated is set as one helical pitch,and plural pitches of the helically turned liquid crystal compound 30are laminated.

The patterned cholesteric liquid crystal layer has wavelength selectivereflection properties.

For example, in a case where the patterned cholesteric liquid crystallayer 26 has a selective reflection center wavelength in a greenwavelength range, the patterned cholesteric liquid crystal layer 26reflects right circularly polarized light G_(R) of green light andallows transmission of the other light.

Here, since the liquid crystal compound 30 rotates to be aligned in aplane direction, the patterned cholesteric liquid crystal layer 26diffracts (refracts) incident circularly polarized light to be reflectedin a direction in which the direction of the optical axis continuouslyrotates. At this time, the diffraction direction varies depending on theturning direction of incident circularly polarized light.

That is, the patterned cholesteric liquid crystal layer 26 reflectsright circularly polarized light or left circularly polarized lighthaving a selective reflection wavelength and diffracts the reflectedlight.

The patterned cholesteric liquid crystal layer 26 is obtained byimmobilizing a cholesteric liquid crystalline phase. That is, thepatterned cholesteric liquid crystal layer 26 is a layer formed of theliquid crystal compound 30 (liquid crystal material) having acholesteric structure.

Cholesteric Liquid Crystalline Phase

It is known that the cholesteric liquid crystalline phase exhibitsselective reflection properties at a specific wavelength. The centerwavelength λ of selective reflection (selective reflection centerwavelength λ) depends on a pitch P (=helical period) of a helicalstructure in the cholesteric liquid crystalline phase and satisfies arelationship of λ = n × P with an average refractive index n of thecholesteric liquid crystalline phase. Therefore, the selectivereflection center wavelength can be adjusted by adjusting the pitch ofthe helical structure. The pitch of the cholesteric liquid crystallinephase depends on the kind of a chiral agent which is used in combinationof a liquid crystal compound during the formation of the cholestericliquid crystal layer, or the concentration of the chiral agent added.Therefore, a desired pitch can be obtained by adjusting the kind andconcentration of the chiral agent.

The details of the adjustment of the pitch can be found in “Fuji FilmResearch&Development” No. 50 (2005), pp. 60 to 63. As a method ofmeasuring a helical sense and a helical pitch, a method described in“Introduction to Experimental Liquid Crystal Chemistry”, (the JapaneseLiquid Crystal Society, 2007, Sigma Publishing Co., Ltd.), p. 46, and“Liquid Crystal Handbook” (the Editing Committee of Liquid CrystalHandbook, Maruzen Publishing Co., Ltd.), p. 196 can be used.

The cholesteric liquid crystalline phase exhibits selective reflectionproperties with respect to left or circularly polarized light at aspecific wavelength. Whether or not the reflected light is rightcircularly polarized light or left circularly polarized light isdetermined depending on a helical twisted direction (sense) of thecholesteric liquid crystalline phase. Regarding the selective reflectionof the circularly polarized light by the cholesteric liquid crystallinephase, in a case where the helical twisted direction of the cholestericliquid crystalline phase is right, right circularly polarized light isreflected, and in a case where the helical twisted direction of thecholesteric liquid crystalline phase is left, left circularly polarizedlight is reflected.

Accordingly, in the optical element 10 shown in the drawing, thecholesteric liquid crystal layer is a layer obtained by immobilizing aright-twisted cholesteric liquid crystalline phase.

A turning direction of the cholesteric liquid crystalline phase can beadjusted by adjusting the kind of the liquid crystal compound that formsthe cholesteric liquid crystal layer and/or the kind of the chiral agentto be added.

In addition, a half-width Δλ (nm) of a selective reflection range(circularly polarized light reflection range) where selective reflectionis exhibited depends on Δn of the cholesteric liquid crystalline phaseand the helical pitch P and complies with a relationship of Δλ = Δn × P.Therefore, the width of the selective reflection range can be controlledby adjusting Δn. Δn can be adjusted by adjusting a kind of a liquidcrystal compound for forming the cholesteric liquid crystal layer and amixing ratio thereof, and a temperature during alignment immobilization.

The half-width of the reflection wavelength range is adjusted dependingon the application of the optical element 10 and is, for example, 10 to500 nm and preferably 20 to 300 nm and more preferably 30 to 100 nm.

Method of Forming Cholesteric Liquid Crystal Layer

The cholesteric liquid crystal layer (patterned cholesteric liquidcrystal layer) can be formed by immobilizing a cholesteric liquidcrystalline phase in a layer shape.

The structure in which a cholesteric liquid crystalline phase isimmobilized may be a structure in which the alignment of the liquidcrystal compound as a cholesteric liquid crystalline phase isimmobilized. Typically, the structure in which a cholesteric liquidcrystalline phase is immobilized is preferably a structure which isobtained by making the polymerizable liquid crystal compound to be in astate where a cholesteric liquid crystalline phase is aligned,polymerizing and curing the polymerizable liquid crystal compound withultraviolet irradiation, heating, or the like to form a layer having nofluidity, and concurrently changing the state of the polymerizableliquid crystal compound into a state where the aligned state is notchanged by an external field or an external force.

The structure in which a cholesteric liquid crystalline phase isimmobilized is not particularly limited as long as the opticalcharacteristics of the cholesteric liquid crystalline phase aremaintained, and the liquid crystal compound 30 in the cholesteric liquidcrystal layer does not necessarily exhibit liquid crystallinity. Forexample, the molecular weight of the polymerizable liquid crystalcompound may be increased by a curing reaction such that the liquidcrystallinity thereof is lost.

Examples of a material used for forming the cholesteric liquid crystallayer obtained by immobilizing a cholesteric liquid crystalline phaseinclude a liquid crystal composition including a liquid crystalcompound. It is preferable that the liquid crystal compound is apolymerizable liquid crystal compound.

In addition, the liquid crystal composition used for forming thecholesteric liquid crystal layer may further include a surfactant and achiral agent.

Polymerizable Liquid Crystal Compound

The polymerizable liquid crystal compound may be a rod-shaped liquidcrystal compound or a disk-shaped liquid crystal compound.

Examples of the rod-shaped polymerizable liquid crystal compound forforming the cholesteric liquid crystalline phase include a rod-shapednematic liquid crystal compound. As the rod-shaped nematic liquidcrystal compound, an azomethine compound, an azoxy compound, acyanobiphenyl compound, a cyanophenyl ester compound, a benzoatecompound, a phenyl cyclohexanecarboxylate compound, acyanophenylcyclohexane compound, a cyano-substituted phenylpyrimidinecompound, an alkoxy-substituted phenylpyrimidine compound, aphenyldioxane compound, a tolan compound, or analkenylcyclohexylbenzonitrile compound is preferably used. Not only alow-molecular-weight liquid crystal compound but also ahigh-molecular-weight liquid crystal compound can be used.

The polymerizable liquid crystal compound can be obtained by introducinga polymerizable group into the liquid crystal compound. Examples of thepolymerizable group include an unsaturated polymerizable group, an epoxygroup, and an aziridinyl group. Among these, an unsaturatedpolymerizable group is preferable, and an ethylenically unsaturatedpolymerizable group is more preferable. The polymerizable group can beintroduced into the molecules of the liquid crystal compound usingvarious methods. The number of polymerizable groups in the polymerizableliquid crystal compound is preferably 1 to 6 and more preferably 1 to 3.

Examples of the polymerizable liquid crystal compound include compoundsdescribed in Makromol. Chem. (1989), Vol. 190, p. 2255, AdvancedMaterials (1993), Vol. 5, p. 107, US4683327A, US5622648A, US5770107A,WO95/022586, WO95/024455, WO97/000600, WO98/023580, WO98/052905,JP1989-272551A (JP-H1-272551A), JP1994-016616A (JP-H6-016616A),JP1995-110469A (JP-H7-110469A), JP1999-080081A (JP-H11-080081A), andJP2001-328973A. Two or more polymerizable liquid crystal compounds maybe used in combination. In a case where two or more polymerizable liquidcrystal compounds are used in combination, the alignment temperature canbe decreased.

In addition, as a polymerizable liquid crystal compound other than theabove-described examples, for example, a cyclic organopolysiloxanecompound having a cholesteric phase described in JP1982-165480A(JP-S57-165480A) can be used. Further, as the above-describedhigh-molecular-weight liquid crystal compound, for example, a polymer inwhich a liquid crystal mesogenic group is introduced into a main chain,a side chain, or both a main chain and a side chain, a polymercholesteric liquid crystal in which a cholesteryl group is introducedinto a side chain, a liquid crystal polymer described in JP1997-133810A(JP-H9-133810A), and a liquid crystal polymer described inJP1999-293252A (JP-H11-293252A) can be used.

Disk-Shaped Liquid Crystal Compound

As the disk-shaped liquid crystal compound, for example, compoundsdescribed in JP2007-108732A and JP2010-244038A can be preferably used.

In addition, the addition amount of the polymerizable liquid crystalcompound in the liquid crystal composition is preferably 75% to 99.9mass%, more preferably 80% to 99 mass%, and still more preferably 85% to90 mass% with respect to the solid content mass (mass excluding asolvent) of the liquid crystal composition.

Surfactant

The liquid crystal composition used for forming the cholesteric liquidcrystal layer may include a surfactant.

It is preferable that the surfactant is a compound that can function asan alignment controller contributing to the stable or rapid formation ofa cholesteric liquid crystalline phase with planar alignment. Examplesof the surfactant include a silicone surfactant and a fluorinesurfactant. Among these, a fluorine surfactant is preferable.

Specific examples of the surfactant include compounds described inparagraphs “0082” to “0090” of JP2014-119605A, compounds described inparagraphs “0031” to “0034” of JP2012-203237A, exemplary compoundsdescribed in paragraphs “0092” and “0093” of JP2005-099248A, exemplarycompounds described in paragraphs “0076” to “0078” and paragraphs “0082”to “0085” of JP2002-129162A, and fluorine (meth)acrylate polymersdescribed in paragraphs “0018” to “0043” of JP2007-272185A.

As the surfactant, one kind may be used alone, or two or more kinds maybe used in combination.

As the fluorine surfactant, a compound described in paragraphs “0082” to“0090” of JP2014-119605A is preferable.

The addition amount of the surfactant in the liquid crystal compositionis preferably 0.01 to 10 mass%, more preferably 0.01 to 5 mass%, andstill more preferably 0.02 to 1 mass% with respect to the total mass ofthe liquid crystal compound.

Chiral Agent (Optically Active Compound)

The chiral agent has a function of causing a helical structure of acholesteric liquid crystalline phase to be formed. The chiral agent maybe selected depending on the purpose because a helical twisted directionor a helical pitch derived from the compound varies.

The chiral agent is not particularly limited, and a well-known compound(for example, Liquid Crystal Device Handbook (No. 142 Committee of JapanSociety for the Promotion of Science, 1989), Chapter 3, Article 4-3,chiral agent for turned nematic (TN) or super turned nematic (STN), p.199), isosorbide, or an isomannide derivative can be used.

In general, the chiral agent includes an asymmetric carbon atom.However, an axially asymmetric compound or a surface asymmetric compoundnot having an asymmetric carbon atom can also be used as a chiral agent.Examples of the axially asymmetric compound or the surface asymmetriccompound include binaphthyl, helicene, paracyclophane, and derivativesthereof. The chiral agent may include a polymerizable group. In a casewhere both the chiral agent and the liquid crystal compound have apolymerizable group, a polymer which includes a repeating unit derivedfrom the polymerizable liquid crystal compound and a repeating unitderived from the chiral agent can be formed due to a polymerizationreaction of a polymerizable chiral agent and the polymerizable liquidcrystal compound. In this aspect, it is preferable that thepolymerizable group included in the polymerizable chiral agent is thesame as the polymerizable group included in the polymerizable liquidcrystal compound. Accordingly, the polymerizable group of the chiralagent is preferably an unsaturated polymerizable group, an epoxy group,or an aziridinyl group, more preferably an unsaturated polymerizablegroup, and still more preferably an ethylenically unsaturatedpolymerizable group.

In addition, the chiral agent may be a liquid crystal compound.

In a case where the chiral agent includes a photoisomerization group, apattern having a desired reflection wavelength corresponding to anemission wavelength can be formed by irradiation of an actinic ray orthe like through a photomask after coating and alignment, which ispreferable. As the photoisomerization group, an isomerization portion ofa photochromic compound, an azo group, an azoxy group, or a cinnamoylgroup is preferable. Specific examples of the compound include compoundsdescribed in JP2002-080478A, JP2002-080851A, JP2002-179668A,JP2002-179669A, JP2002-179670A, JP2002-179681A, JP2002-179682A,JP2002-338575A, JP2002-338668A, JP2003-313189A, and JP2003-313292A.

Photoreactive Chiral Agent

In the present invention, it is preferable that a photoreactive chiralagent is used as the chiral agent. The photoreactive chiral agent isformed of, for example, a compound represented by the following Formula(I) and has properties capable of controlling an aligned structure ofthe liquid crystal compound and changing a helical pitch of liquidcrystal, that is, a helical twisting power (HTP) of a helical structureduring light irradiation. That is, the photoreactive chiral agent is acompound that causes a helical twisting power of a helical structurederived from a liquid crystal compound, preferably, a nematic liquidcrystal compound to change during light irradiation (ultraviolet lightto visible light to infrared light), and includes a portion including achiral portion and a portion in which a structural change occurs duringlight irradiation as necessary portions (molecular structural units).However, the photoreactive chiral agent represented by the followingFormula (I) can significantly change the HTP of liquid crystalmolecules.

The above-described HTP represents the helical twisting power of ahelical structure of liquid crystal, that is, HTP = 1/(Pitch × ChiralAgent Concentration [Mass Fraction]). For example, the HTP can beobtained by measuring a helical pitch (single period of the helicalstructure; µm) of a liquid crystal molecule at a given temperature andconverting the measured value into a value [µm⁻¹] in terms of theconcentration of the chiral agent. In a case where a selectivereflection color is formed by the photoreactive chiral agent dependingon the illuminance of light, a change ratio in HTP (HTP beforeirradiation/HTP after irradiation) is preferably 1.5 or higher and morepreferably 2.5 or higher in a case where the HTP decreases afterirradiation, and is preferably 0.7 or lower and more preferably 0.4 orlower in a case where the HTP increases after irradiation.

Next, the compound represented by Formula (I) will be described.

In the formula, R represents a hydrogen atom, an alkoxy group having 1to 15 carbon atoms, an acryloyloxyalkyloxy group having 3 to 15 carbonatoms in total, or a methacryloyloxyalkyloxy group having 4 to 15 carbonatoms in total.

Examples of the alkoxy group having 1 to 15 carbon atoms include amethoxy group, an ethoxy group, a propoxy group, a butoxy group, ahexyloxy group, and a dodecyloxy group. In particular, an alkoxy grouphaving 1 to 12 carbon atoms is preferable, and an alkoxy group having 1to 8 carbon atoms is more preferable.

Examples of the acryloyloxyalkyloxy group having 3 to 15 carbon atoms intotal include an acryloyloxyethyloxy group, an acryloyloxybutyloxygroup, and an acryloyloxydecyloxy group. In particular, anacryloyloxyalkyloxy group having 5 to 13 carbon atoms is preferable, andan acryloyloxyalkyloxy group having 5 to 11 carbon atoms is morepreferable.

Examples of the methacryloyloxyalkyloxy group having 4 to 15 carbonatoms in total include a methacryloyloxyethyloxy group, amethacryloyloxybutyloxy group, and a methacryloyloxydecyloxy group. Inparticular, a methacryloyloxyalkyloxy group having 6 to 14 carbon atomsis preferable, and a methacryloyloxyalkyloxy group having 6 to 12 carbonatoms is more preferable.

The molecular weight of the photoreactive chiral agent represented byFormula (I) is preferably 300 or higher. In addition, it is preferablethat the solubility in the liquid crystal compound described below ishigh, and it is more preferable that the solubility parameter SP valueis close to that of the liquid crystal compound.

Hereinafter, specific examples (exemplary compounds (1) to (15)) of thecompound represented by Formula (I) will be shown, but the presentinvention is not limited thereto.

In the present invention, as the photoreactive chiral agent, forexample, a photoreactive optically active compound represented by thefollowing Formula (II) is also used.

In the formula, R represents a hydrogen atom, an alkoxy group having 1to 15 carbon atoms, an acryloyloxyalkyloxy group having 3 to 15 carbonatoms in total, or a methacryloyloxyalkyloxy group having 4 to 15 carbonatoms in total.

Examples of the alkoxy group having 1 to 15 carbon atoms include amethoxy group, an ethoxy group, a propoxy group, a butoxy group, ahexyloxy group, an octyloxy group, and a dodecyloxy group. Inparticular, an alkoxy group having 1 to 10 carbon atoms is preferable,and an alkoxy group having 1 to 8 carbon atoms is more preferable.

Examples of the acryloyloxyalkyloxy group having 3 to 15 carbon atoms intotal include an acryloyloxy group, an acryloyloxyethyloxy group, anacryloyloxypropyloxy group, an acryloyloxyhexyloxy group, anacryloyloxybutyloxy group, and an acryloyloxydecyloxy group. Inparticular, an acryloyloxyalkyloxy group having 3 to 13 carbon atoms ispreferable, and an acryloyloxyalkyloxy group having 3 to 11 carbon atomsis more preferable.

Examples of the methacryloyloxyalkyloxy group having 4 to 15 carbonatoms in total include a methacryloyloxy group, amethacryloyloxyethyloxy group, and a methacryloyloxyhexyloxy group. Inparticular, a methacryloyloxyalkyloxy group having 4 to 14 carbon atomsis preferable, and a methacryloyloxyalkyloxy group having 4 to 12 carbonatoms is more preferable.

The molecular weight of the photoreactive optically active compoundrepresented by Formula (II) is preferably 300 or higher. In addition, itis preferable that the solubility in the liquid crystal compounddescribed below is high, and it is more preferable that the solubilityparameter SP value is close to that of the liquid crystal compound.

Hereinafter, specific examples (exemplary compounds (21) to (32)) of thephotoreactive optically active compound represented by Formula (II) willbe shown, but the present invention is not limited thereto.

In addition, the photoreactive chiral agent can also be used incombination with a chiral agent having no photoreactivity such as achiral compound having a large temperature dependence of the helicaltwisting power. Examples of the well-known chiral agent having nophotoreactivity include chiral agents described in JP2000-044451A,JP1998-509726A (JP-H10-509726A), WO1998/000428A, JP2000-506873A,JP1997-506088A(JP-H09-506088A), Liquid Crystals (1996, 21, 327), andLiquid Crystals (1998, 24, 219).

The content of the chiral agent in the liquid crystal composition ispreferably 0.01% to 200 mol% and more preferably 1% to 30 mol% withrespect to the content molar amount of the liquid crystal compound.

Polymerization Initiator

In a case where the liquid crystal composition includes a polymerizablecompound, it is preferable that the liquid crystal composition includesa polymerization initiator. In an aspect where a polymerization reactionprogresses with ultraviolet irradiation, it is preferable that thepolymerization initiator is a photopolymerization initiator whichinitiates a polymerization reaction with ultraviolet irradiation.

Examples of the photopolymerization initiator include an α-carbonylcompound (described in US2367661A and US2367670A), an acyloin ether(described in US2448828A), an α-hydrocarbon-substituted aromatic acyloincompound (described in US2722512A), a polynuclear quinone compound(described in US3046127A and US2951758A), a combination of atriarylimidazole dimer and p-aminophenyl ketone (described inUS3549367A), an acridine compound and a phenazine compound (described inJP1985-105667A (JP-S60-105667A) and US4239850A), and an oxadiazolecompound (described in US4212970A).

The content of the photopolymerization initiator in the liquid crystalcomposition is preferably 0.1 to 20 mass% and more preferably 0.5 to 12mass% with respect to the content of the liquid crystal compound.

Crosslinking Agent

In order to improve the film hardness after curing and to improvedurability, the liquid crystal composition may optionally include acrosslinking agent. As the crosslinking agent, a curing agent which canperform curing with ultraviolet light, heat, moisture, or the like canbe preferably used.

The crosslinking agent is not particularly limited and can beappropriately selected depending on the purpose. Examples of thecrosslinking agent include: a polyfunctional acrylate compound such astrimethylol propane tri(meth)acrylate or pentaerythritoltri(meth)acrylate; an epoxy compound such as glycidyl (meth)acrylate orethylene glycol diglycidyl ether; an aziridine compound such as 2,2-bishydroxymethyl butanol-tris[3-(1-aziridinyl)propionate] or4,4-bis(ethyleneiminocarbonylamino)diphenylmethane; an isocyanatecompound such as hexamethylene diisocyanate or a biuret type isocyanate;a polyoxazoline compound having an oxazoline group at a side chainthereof; and an alkoxysilane compound such as vinyl trimethoxysilane orN-(2-aminoethyl)-3-aminopropyltrimethoxysilane. In addition, dependingon the reactivity of the crosslinking agent, a well-known catalyst canbe used, and not only film hardness and durability but also productivitycan be improved. Among these crosslinking agents, one kind may be usedalone, or two or more kinds may be used in combination.

The content of the crosslinking agent is preferably 3% to 20 mass% andmore preferably 5% to 15 mass% with respect to the solid content mass ofthe liquid crystal composition. In a case where the content of thecrosslinking agent is in the above-described range, an effect ofimproving a crosslinking density can be easily obtained, and thestability of a cholesteric liquid crystalline phase is further improved.

Other Additives

Optionally, a polymerization inhibitor, an antioxidant, an ultravioletabsorber, a light stabilizer, a coloring material, metal oxideparticles, or the like can be added to the liquid crystal composition ina range where optical performance and the like do not deteriorate.

In a case where the cholesteric liquid crystal layer is formed, it ispreferable that the liquid crystal composition is used as liquid.

The liquid crystal composition may include a solvent. The solvent is notparticularly limited and can be appropriately selected depending on thepurpose. An organic solvent is preferable.

The organic solvent is not particularly limited and can be appropriatelyselected depending on the purpose. Examples of the organic solventinclude a ketone, an alkyl halide, an amide, a sulfoxide, a heterocycliccompound, a hydrocarbon, an ester, and an ether. Among these organicsolvents, one kind may be used alone, or two or more kinds may be usedin combination. Among these, a ketone is preferable in consideration ofan environmental burden.

In a case where the cholesteric liquid crystal layer is formed, it ispreferable that the cholesteric liquid crystal layer is formed byapplying the liquid crystal composition to a surface where thecholesteric liquid crystal layer is to be formed, aligning the liquidcrystal compound to a state of a cholesteric liquid crystalline phase,and curing the liquid crystal compound.

That is, in a case where the cholesteric liquid crystal layer is formedon the alignment film, it is preferable that the cholesteric liquidcrystal layer obtained by immobilizing a cholesteric liquid crystallinephase is formed by applying the liquid crystal composition to thealignment film, aligning the liquid crystal compound to a state of acholesteric liquid crystalline phase, and curing the liquid crystalcompound.

For the application of the liquid crystal composition, a printing methodsuch as ink jet or scroll printing or a well-known method such as spincoating, bar coating, or spray coating capable of uniformly applyingliquid to a sheet-shaped material can be used.

The applied liquid crystal composition is optionally dried and/or heatedand then is cured to form the cholesteric liquid crystal layer. In thedrying and/or heating step, the liquid crystal compound in the liquidcrystal composition only has to be aligned to a cholesteric liquidcrystalline phase. In the case of heating, the heating temperature ispreferably 200° C. or lower and more preferably 130° C. or lower.

The aligned liquid crystal compound is optionally further polymerized.Regarding the polymerization, thermal polymerization orphotopolymerization using light irradiation may be performed, andphotopolymerization is preferable. Regarding the light irradiation,ultraviolet light is preferably used. The irradiation energy ispreferably 20 mJ/cm² to 50 J/cm² and more preferably 50 to 1500 mJ/cm².In order to promote a photopolymerization reaction, light irradiationmay be performed under heating conditions or in a nitrogen atmosphere.The wavelength of irradiated ultraviolet light is preferably 250 to 430nm.

The thickness of the cholesteric liquid crystal layer is notparticularly limited, and the thickness with which a required lightreflectivity can be obtained may be appropriately set depending on theuse of the optical element 10, the light reflectivity required for thecholesteric liquid crystal layer, the material for forming thecholesteric liquid crystal layer, and the like.

Liquid Crystal Alignment Pattern of Patterned Cholesteric Liquid CrystalLayer

In the optical element 10 according to the embodiment of the presentinvention, the patterned cholesteric liquid crystal layer has the liquidcrystal alignment pattern in which the direction of the optical axis 30Aderived from the liquid crystal compound 30 forming the cholestericliquid crystalline phase changes while continuously rotating in thein-plane direction of the patterned cholesteric liquid crystal layer.

The optical axis 30A derived from the liquid crystal compound 30 is anaxis having the highest refractive index in the liquid crystal compound30, that is, a so-called slow axis. For example, in a case where theliquid crystal compound 30 is a rod-shaped liquid crystal compound, theoptical axis 30A is along a rod-shaped major axis direction. In thefollowing description, the optical axis 30A derived from the liquidcrystal compound 30 will also be referred to as “the optical axis 30A ofthe liquid crystal compound 30” or “the optical axis 30A”.

FIG. 14 is a plan view conceptually showing the patterned cholestericliquid crystal layer 26.

The plan view is a view in a case where the optical element 10 is seenfrom the top in FIG. 12 , that is, a view in a case where the opticalelement 10 is seen from a thickness direction (laminating direction ofthe respective layers (films)).

In addition, as described above, in FIG. 14 , in order to clarify theconfiguration of the optical element 10 according to the embodiment ofthe present invention, as in FIG. 12 , only the liquid crystal compound30 on the surface of the alignment film 24 is shown.

FIG. 14 shows the patterned cholesteric liquid crystal layer 26 as arepresentative example. However, basically, a patterned cholestericliquid crystal layer described below also has the same configuration andthe same effects as those of the patterned cholesteric liquid crystallayer 26, except that the lengths A of the single periods of the liquidcrystal alignment patterns described below or the reflection wavelengthranges are different from each other.

As shown in FIG. 14 , on the surface of the alignment film 24, theliquid crystal compound 30 forming the patterned cholesteric liquidcrystal layer 26 is two-dimensionally arranged according to thealignment pattern formed on the alignment film 24 as the lower layer ina predetermined in-plane direction indicated by arrow X and a directionperpendicular to the in-plane direction (arrow X direction).

In the following description, the direction perpendicular to the arrow Xdirection will be referred to as “Y direction” for convenience ofdescription. That is, in FIGS. 12 and 13 and FIG. 15 described below,the Y direction is a direction perpendicular to the paper plane.

In addition, the liquid crystal compound 30 forming the patternedcholesteric liquid crystal layer 26 has the liquid crystal alignmentpattern in which the direction of the optical axis 30A changes whilecontinuously rotating in the arrow X direction in a plane of thepatterned cholesteric liquid crystal layer 26. In the example shown inthe drawing, the liquid crystal compound 30 has the liquid crystalalignment pattern in which the optical axis 30A of the liquid crystalcompound 30 changes while continuously rotating clockwise in the arrow Xdirection.

Specifically, “the direction of the optical axis 30A of the liquidcrystal compound 30 changes while continuously rotating in the arrow Xdirection (the predetermined in-plane direction)” represents that anangle between the optical axis 30A of the liquid crystal compound 30,which is arranged in the arrow X direction, and the arrow X directionvaries depending on positions in the arrow X direction, and the anglebetween the optical axis 30A and the arrow X direction sequentiallychanges from θ to Y or θ-180° in the arrow X direction.

A difference between the angles of the optical axes 30A of the liquidcrystal compound 30 adjacent to each other in the arrow X direction ispreferably 45° or less, more preferably 15° or less, and still morepreferably less than 15°.

On the other hand, in the liquid crystal compound 30 forming thepatterned cholesteric liquid crystal layer 26, the directions of theoptical axes 30A are the same in the Y direction perpendicular to thearrow X direction, that is, the Y direction perpendicular to thein-plane direction in which the optical axis 30A continuously rotates.

In other words, in the liquid crystal compound 30 forming the patternedcholesteric liquid crystal layer 26, angles between the optical axes 30Aof the liquid crystal compound 30 and the arrow X direction are the samein the Y direction.

In the optical element 10 according to the embodiment of the presentinvention, in the liquid crystal alignment pattern of the liquid crystalcompound 30, the length (distance) over which the optical axis 30A ofthe liquid crystal compound 30 rotates by 180° in the arrow X directionin which the optical axis 30A changes while continuously rotating in aplane is the length A of the single period in the liquid crystalalignment pattern.

That is, a distance between centers of two liquid crystal compounds 30in the arrow X direction is the length A of the single period, the twoliquid crystal compounds having the same angle in the arrow X direction.Specifically, as shown in FIG. 14 , a distance of centers in the arrow Xdirection of two liquid crystal compounds 30 in which the arrow Xdirection and the direction of the optical axis 30A match each other isthe length Λ of the single period.

In the following description, the length Λ of the single period willalso be referred to as “single period Λ”.

In the optical element 10 according to the embodiment of the presentinvention, in the liquid crystal alignment pattern of the patternedcholesteric liquid crystal layer, the single period A is repeated in thearrow X direction, that is, in the in-plane direction in which thedirection of the optical axis 30A changes while continuously rotating.

The patterned cholesteric liquid crystal layer 26 has the liquid crystalalignment pattern in which the optical axis 30A changes whilecontinuously rotating in the arrow X direction in a plane (thepredetermined in-plane direction).

The cholesteric liquid crystal layer obtained by immobilizing acholesteric liquid crystalline phase typically reflects incident light(circularly polarized light) by specular reflection.

On the other hand, the patterned cholesteric liquid crystal layer 26having the above-described liquid crystal alignment pattern reflectsincidence light in a direction having an angle in the arrow X directionwith respect to specular reflection. For example, in the patternedcholesteric liquid crystal layer 26, light incident from the normaldirection is reflected in a state where it is tilted as indicated by thearrow X with respect to the normal direction instead of being reflectedin the normal direction. That is, the light incident from the normaldirection refers to light incident from the front side that is lightincident to be perpendicular to a main surface. The main surface refersto the maximum surface of a sheet-shaped material.

Hereinafter, the description will be made with reference to FIG. 15 .

As described above, the patterned cholesteric liquid crystal layer 26selectively reflects one circularly polarized light in a selectivereflection wavelength. For example, a case where the selectivereflection wavelength of the patterned cholesteric liquid crystal layer26 is green light and right circularly polarized light is reflected willbe described. The patterned cholesteric liquid crystal layer 26selectively reflects right circularly polarized light G_(R) of greenlight.

Accordingly, in a case where light is incident into the first reflectinglayer 14, the patterned cholesteric liquid crystal layer 26 reflectsonly right circularly polarized light G_(R) of green light and allowstransmission of the other light.

In a case where the right circularly polarized light G_(R) of greenlight incident into the patterned cholesteric liquid crystal layer 26 isreflected from the patterned cholesteric liquid crystal layer 26, theabsolute phase changes depending on the directions of the optical axes30A of the respective liquid crystal compounds 30.

Here, in the patterned cholesteric liquid crystal layer 26, the opticalaxis 30A of the liquid crystal compound 30 changes while rotating in thearrow X direction (the in-plane direction). Therefore, the amount ofchange in the absolute phase of the incident right circularly polarizedlight G_(R) of green light varies depending on the directions of theoptical axes 30A.

Further, the liquid crystal alignment pattern formed in the patternedcholesteric liquid crystal layer 26 is a pattern that is periodic in thearrow X direction. Therefore, as conceptually shown in FIG. 15 , anabsolute phase Q that is periodic in the arrow X direction correspondingto the direction of the optical axis 30A is assigned to the rightcircularly polarized light G_(R) of green light incident into thepatterned cholesteric liquid crystal layer 26.

In addition, the direction of the optical axis 30A of the liquid crystalcompound 30 with respect to the arrow X direction is uniform in thearrangement of the liquid crystal compound 30 in the Y directionperpendicular to arrow X direction.

As a result, in the patterned cholesteric liquid crystal layer 26, anequiphase surface E that is tilted in the arrow X direction with respectto an XY plane is formed for the right circularly polarized light G_(R)of green light.

Therefore, the right circularly polarized light G_(R) of green light isreflected in the normal direction of the equiphase surface E (directionperpendicular to the equiphase surface E), and the reflected rightcircularly polarized light G_(R) of green light is reflected in adirection that is tilted in the arrow X direction with respect to the XYplane (main surface of the patterned cholesteric liquid crystal layer26).

Here, a reflection angle of light from the patterned cholesteric liquidcrystal layer in which the optical axis 30A of the liquid crystalcompound 30 continuously rotates in the in-plane direction (arrow Xdirection) varies depending on wavelengths of light to be reflected.Specifically, as the wavelength of light increases, the angle ofreflected light with respect to incidence light increases.

On the other hand, a reflection angle of light from the patternedcholesteric liquid crystal layer in which the optical axis 30A of theliquid crystal compound 30 continuously rotates in the arrow X direction(in-plane direction) varies depending on the length Λ of the singleperiod of the liquid crystal alignment pattern over which the opticalaxis 30A rotates by 180° in the arrow X direction, that is, depending onthe single period Λ. Specifically, as the length of the single period Λdecreases, the angle of reflected light with respect to incidence lightincreases.

This point will be described below.

In the optical element 10 according to the embodiment of the presentinvention, the single period Λ in the alignment pattern of the patternedcholesteric liquid crystal layer is not particularly limited and may beappropriately set depending on the use of the optical element 10 and thelike.

Here, the optical element 10 according to the embodiment of the presentinvention can be suitably used as, for example, a diffraction elementthat reflects light displayed by a display to be introduced into a lightguide plate in AR glasses or a diffraction element that emits lightpropagated in a light guide plate to an observation position by a userfrom the light guide plate.

At this time, in order to totally reflect light from the light guideplate, it is necessary to reflect light to be introduced into the lightguide plate at a large angle to some degree with respect to incidencelight. In addition, in order to reliably emit light propagated in thelight guide plate, it is necessary to reflect at a large angle to somedegree with respect to incidence light.

In addition, as described above, the reflection angle from the patternedcholesteric liquid crystal layer with respect to incidence light can beincreased by reducing the single period A in the liquid crystalalignment pattern.

In consideration of this point, the single period A in the liquidcrystal alignment pattern of the patterned cholesteric liquid crystallayer is preferably 50 µm or less, more preferably 10 µm or less, andstill more preferably 1 µm or less.

In consideration of the accuracy of the liquid crystal alignment patternand the like, the single period A in the liquid crystal alignmentpattern of the patterned cholesteric liquid crystal layer is preferably0.1 µm or more.

Here, in the optical element according to the embodiment of the presentinvention, the patterned cholesteric liquid crystal layer has the liquidcrystal alignment pattern in which the direction of the optical axis 30Aderived from the liquid crystal compound 30 forming the cholestericliquid crystalline phase changes while continuously rotating in thein-plane direction of the patterned cholesteric liquid crystal layer.

In addition, in the optical element according to the embodiment of thepresent invention, as conceptually shown in FIG. 12 , the patternedcholesteric liquid crystal layer has regions having different pitches ofhelical structures in a plane.

Further, in the optical element according to the embodiment of thepresent invention, as conceptually shown in FIG. 12 , the patternedcholesteric liquid crystal layer has regions having different lengths Λof the single periods in the liquid crystal alignment pattern in aplane.

In the configuration of the optical element 10 shown in FIG. 12 , thepatterned cholesteric liquid crystal layer 26 of the first reflectinglayer 14 has a liquid crystal alignment pattern in which a direction ofan optical axis derived from a liquid crystal compound changes whilecontinuously rotating in at least one in-plane direction, the patternedcholesteric liquid crystal layer has regions having different pitches ofhelical structures in a plane, and the patterned cholesteric liquidcrystal layer has regions having different lengths Λ of the singleperiods in the liquid crystal alignment pattern in a plane. That is, thereflecting layer in the present invention is configured.

Specifically, the patterned cholesteric liquid crystal layer 26 in FIG.12 is configured such that a helical pitch PT₂ in the right side regionof FIG. 12 is longer than a helical pitch PT₀ in the left side region ofFIG. 12 and a helical pitch PT₁ (not shown) in the intermediate regionin the left-right direction in FIG. 12 is longer than the helical pitchPT₀ and is shorter than the helical pitch PT₂. That is, the helicalpitch increases from the left side region toward the right side regionin FIG. 12 .

The helical pitch is the distance over which the liquid crystal compoundrotates helically once (360° rotation). In FIG. 12 , schematically,distances over which the liquid crystal compound rotates half a rotation(180° rotation) are represented by PT₀ and PT₂.

In addition, in the patterned cholesteric liquid crystal layer 26 inFIG. 12 , a length Λ_(A2) of the single period of the right side regionin FIG. 12 is shorter than a length Λ_(A0) of the single period of theleft side region in FIG. 12 , and a length Λ_(A1) of the single periodof the center region in the left-right direction in FIG. 12 is shorterthan the length Λ_(A0) of the single period and is longer than thelength Λ_(A2) of the single period. That is, the length Λ of the singleperiod decreases from the left side region toward the right side regionin FIG. 12 .

Hereinafter, the optical element according to the embodiment of thepresent invention will be described in more detail by describing theaction of the optical element 10 according to the embodiment of thepresent invention with reference to FIG. 17 .

In FIG. 17 , in order to clarify the action of the optical element 10,only the patterned cholesteric liquid crystal layer 26 is shown insteadof the entirety of the first reflecting layer 14. In addition, due tothe same reason, light is incident from the normal direction (frontside) into the optical element 10.

As described above, the patterned cholesteric liquid crystal layer 26selectively reflects right circularly polarized light G_(R) of greenlight and allows transmission of the other light.

In addition, in the portion shown in FIG. 17 , the patterned cholestericliquid crystal layer 26 includes three regions A0, A1, A2 in order fromthe left side in FIG. 17 , and the respective regions have differentlengths of helical pitches and different lengths Λ of single periods.Specifically, the helical pitch increases in order of the regions A0,A1, and A2, and the length A of the single period decreases in order ofthe regions A0, A1, and A2.

In the optical element 10, in a case where right circularly polarizedlight G_(R1) of green light is incident into an in-plane region A1 ofthe patterned cholesteric liquid crystal layer 26, as described above,the light is reflected in a direction that is tilted by a predeterminedangle in the arrow X direction, that is, in the in-plane direction inwhich the direction of the optical axis of the liquid crystal compoundchanges while continuously rotating with respect to the incidencedirection. Likewise, in a case where right circularly polarized lightG_(R2) of green light is incident into an in-plane region A2 of thepatterned cholesteric liquid crystal layer 26, the light is reflected ina direction that is tilted by a predetermined angle in the arrow Xdirection with respect to the incidence direction. Likewise, in a casewhere the right circularly polarized light G_(R2) of green light isincident into an in-plane region A0 of the patterned cholesteric liquidcrystal layer 26, the light is reflected in a direction that is tiltedby a predetermined angle in the arrow X direction with respect to theincidence direction.

Here, as described above, the patterned cholesteric liquid crystal layer26 has the liquid crystal alignment pattern in which the optical axis30A derived from the liquid crystal compound 30 changes whilecontinuously rotating clockwise in the arrow X direction.

Regarding the reflection angles from the patterned cholesteric liquidcrystal layer 26, since a single period Λ_(A2) of the liquid crystalalignment pattern of the region A2 is shorter than a single periodΛ_(A1) of the liquid crystal alignment pattern of the region A1, asshown in FIG. 17 , a reflection angle θ_(A2) of reflected light of theregion A2 is more than a reflection angle θ_(A1) of reflected light ofthe region A1 with respect to the incidence light. In addition, since asingle period Λ_(A0) of the liquid crystal alignment pattern of theregion A0 is longer than the single period Λ_(A1) of the liquid crystalalignment pattern of the region A1, as shown in FIG. 17 , a reflectionangle θ_(A0) of reflected light of the region A0 is less than thereflection angle θ_(A1) of reflected light of the region A1 with respectto the incidence light.

Here, in the reflection of light from the cholesteric liquid crystallayer, a so-called blue shift (short-wavelength shift) in which thewavelength of light to be selectively reflected shifts to a shortwavelength side occurs depending on angles of incidence light.Therefore, in the cholesteric liquid crystal layer that has a liquidcrystal alignment pattern in which a direction of an optical axisderived from a liquid crystal compound changes while continuouslyrotating in at least one in-plane direction, there is a problem in thatthe amount of light reflected decreases due to influence of blue shift(short-wavelength shift) as the reflection angle increases. Therefore,in a case where the patterned cholesteric liquid crystal layer hasregions having different lengths of the single periods over which thedirection of the optical axis of the liquid crystal compound rotates by180° in a plane, the reflection angle varies depending on lightincidence positions. Therefore, there is a difference in the amount oflight reflected depending on in-plane incidence positions. That is, itwas found that there is a problem in that a region where the brightnessof light reflected is low depending on in-plane incidence positions ispresent.

Accordingly, in the example shown in FIG. 17 , the amount of reflectedlight in the region A1 is less than the amount of reflected light in theregion A0, and the amount of reflected light in the region A2 is lessthan the amount of reflected light in the region A1.

On the other hand, in the optical element according to the embodiment ofthe present invention, the patterned cholesteric liquid crystal layerhas regions having different helical pitches in a plane.

In the example shown in FIG. 17 , in the patterned cholesteric liquidcrystal layer 26, a length PL_(A2) of the pitch of the helical structurein the region A2 is more than a length PL_(A1) of the pitch of thehelical structure in the region A1, and a length PL_(A0) of the pitch ofthe helical structure in the region A0 is more than the length PL_(A1)of the pitch of the helical structure in the region A1.

As a result, the influence of blue shift in which the wavelength oflight to be selectively reflected shifts to a short wavelength side canbe reduced, and a decrease in the amount of reflected light in theregion where the reflection angle of reflected light is large can besuppressed. Specifically, by increasing the length of the pitch of thehelical structure such that the selective reflection wavelength duringblue shift is the same as the wavelength of light to be incident, thereflection efficiency at the wavelength of light to be incident can beincreased. Accordingly, the generation of a region where the brightnessof light reflected is low depending on in-plane incidence positions canbe suppressed.

In the example shown in FIG. 17 , the helical pitch PL_(A1) in theregion A1 where the reflection angle θ_(A1) of reflected light is lessthan that in the region A0, that is, the length Λ_(A1) of the singleperiod is shorter than the length Λ_(A0) of the single period in theregion A0 is set to be longer than the helical pitch PL_(A0) in theregion A0. In addition, the helical pitch PL_(A2) in the region A2 wherethe reflection angle θ_(A2) of reflected light is the largest, that is,the length Λ_(A2) of the single period is the shortest is set to belonger than the helical pitch in the region A0 and the helical pitch inthe region A1. As a result, a decrease in the amount of light reflectedfrom the regions A1 and A2 can be suppressed, and the amounts of lightreflected from in-plane incidence positions can be made to be uniform.

This way, in the optical element 10 according to the embodiment of thepresent invention, in an in-plane region where the reflection angle fromthe patterned cholesteric liquid crystal layer is large, incidence lightis reflected from a region where the pitch of the helical structure islong. On the other hand, in an in-plane region where the reflectionangle from the patterned cholesteric liquid crystal layer is small,incidence light is reflected from a region where the pitch of thehelical structure is short.

That is, in the optical element 10, by setting the length of the pitchof the helical structure in a plane according to the size of thereflection angle from the patterned cholesteric liquid crystal layer,the brightness of reflected light with respect to incidence light can beincreased.

Therefore, in the optical element 10 according to the embodiment of thepresent invention, the reflection angle dependence of the amount oflight reflected in a plane can be reduced.

As described above, the angle of reflected light in a plane of thepatterned cholesteric liquid crystal layer 26 increases as the singleperiod A of the liquid crystal alignment pattern decreases.

In addition, the length of the pitch of the helical structure in a planeof the patterned cholesteric liquid crystal layer 26 in the region wherethe length of the single period Λ over which the direction of theoptical axis 30A rotates by 180° in the arrow X direction in the liquidcrystal alignment pattern is short is longer than that in the regionwhere the single period A is long. In the optical element 10, forexample, as shown in FIG. 17 , the single period Λ_(A2) of the liquidcrystal alignment pattern in the region A2 of the patterned cholestericliquid crystal layer 26 is shorter than the single period Λ_(A1) of theliquid crystal alignment pattern in the region A1, and the lengthPL_(A2) of the pitch of the helical structure is long. That is, in theregion A2 of the patterned cholesteric liquid crystal layer 26, a largeamount of light is reflected.

Accordingly, by setting the length PL of the pitch of the helicalstructure in a plane with respect to the single period Λ of the liquidcrystal alignment pattern as a target, the brightness of light reflectedfrom different in-plane regions at different angles can be suitablyincreased.

In the optical element according to the embodiment of the presentinvention, as described above, the length of the single period Λ of theliquid crystal alignment pattern decreases, the reflection angleincreases. Therefore, by setting the length PL of the pitch of thehelical structure to be long in the region where the length of thesingle period Λ of the liquid crystal alignment pattern is short, thebrightness of reflected light can be increased.

Therefore, in the optical element according to the embodiment of thepresent invention, in regions having different lengths of single periodsof liquid crystal alignment patterns, it is preferable that apermutation of the lengths of the single periods and a permutation ofthe lengths of the pitches of the helical structures are different fromeach other.

However, the present invention is not limited to this configuration. Inthe optical element according to the embodiment of the presentinvention, in regions having different lengths of single periods ofliquid crystal alignment patterns, a permutation of the lengths of thesingle periods and a permutation of the lengths of the pitches of thehelical structures may be the same as each other. In the optical elementaccording to the embodiment of the present invention, the length of thepitch of the helical structure has a preferable range and may beappropriately set according to the single period Λ of the liquid crystalalignment pattern in a plane.

In the patterned cholesteric liquid crystal layer (cholesteric liquidcrystal layer) according to the embodiment of the present inventionhaving a liquid crystal alignment pattern in which a direction of anoptical axis derived from a liquid crystal compound changes whilecontinuously rotating in at least one in-plane direction, by adjusting apitch of a helical structure in the cholesteric liquid crystallinephase, a slope pitch of tilted surfaces of bright portions and darkportions with respect to a main surface in a case where a cross-sectionof the patterned cholesteric liquid crystal layer is observed with ascanning electron microscope (SEM) (an interval between bright portionsor between dark portions in the normal direction with respect to theslope is set as ½ surface pitch) can be adjusted, and the selectivereflection center wavelength with respect to oblique light can beadjusted.

Here, in the example shown in FIG. 12 , the optical element 10 includesone patterned cholesteric liquid crystal layer, but the presentinvention is not limited thereto. The optical element may include two ormore patterned cholesteric liquid crystal layers. In addition, theoptical element may include one or more patterned cholesteric liquidcrystal layers and one or more cholesteric liquid crystal layers in therelated art.

In addition, in a case where the optical element according to theembodiment of the present invention includes two or more patternedcholesteric liquid crystal layers, the optical element may includepatterned cholesteric liquid crystal layers having different directions(senses of helical structures) of circularly polarized light to bereflected.

For example, an optical element 10 b shown in FIG. 22 has aconfiguration in which two patterned cholesteric liquid crystal layershaving different directions (senses of helical structures) of circularlypolarized light to be reflected are laminated. In FIG. 22 , thepatterned cholesteric liquid crystal layer 26 has the same configurationas that of the patterned cholesteric liquid crystal layer 26 shown inFIG. 12 and the like. On the other hand, a (second) patternedcholesteric liquid crystal layer 26 b has the same configuration as thatof the patterned cholesteric liquid crystal layer 26, except that thepatterned cholesteric liquid crystal layer 26 b has a rotation directionopposite to the rotation direction of the helical structure in thepatterned cholesteric liquid crystal layer 26. That is, the patternedcholesteric liquid crystal layer 26 b has a liquid crystal alignmentpattern in which a direction of an optical axis of a liquid crystalcompound rotates in one in-plane direction, has regions having differentpitches of helical structures in a plane, and has regions havingdifferent lengths Λ of the single periods of the liquid crystalalignment patterns.

This way, the optical element further includes reflection cholestericliquid crystal layers having different directions (senses of helicalstructures) of circularly polarized light to be reflected such thatincidence light in various polarization states can be efficientlyreflected.

Here, in a case where the optical element includes a plurality ofpatterned cholesteric liquid crystal layers having different directionsof circularly polarized light to be reflected, it is preferable that theselective reflection center wavelengths are the same (substantially thesame).

This way, by providing the patterned cholesteric liquid crystal layershaving the same selective reflection center wavelength and differentdirections of circularly polarized light to be reflected, a reflectivityof specific light can be improved.

Here, in the patterned cholesteric liquid crystal layers having the sameselective reflection center wavelength and different directions ofcircularly polarized light to be reflected, it is preferable that therotation directions of the optical axes 30A of the liquid crystalcompound 30 in the liquid crystal alignment pattern are different fromeach other.

For example, in a case where the rotation direction of the optical axis30A of the liquid crystal compound 30 in the patterned cholestericliquid crystal layer 26 that reflects right circularly polarized lightof green light is clockwise as shown in FIG. 14 , it is preferable thatthe rotation direction of the optical axis 30A of the liquid crystalcompound 30 in the second patterned cholesteric liquid crystal layer 26b that reflects left circularly polarized light of green light iscounterclockwise.

In the cholesteric liquid crystal layers in which the optical axis 30Aof the liquid crystal compound 30 continuously rotates in the arrow Xdirection (the in-plane direction), in a case where the directions ofcircularly polarized light are different from each other and therotation directions of the optical axes 30A are the same, a reflectiondirection of circularly polarized light in the patterned cholestericliquid crystal layer that reflects right circularly polarized light isopposite to that in the patterned cholesteric liquid crystal layer thatreflects left circularly polarized light.

On the other hand, in the patterned cholesteric liquid crystal layershaving the same selective reflection center wavelength and differentdirections of circularly polarized light to be reflected, by setting therotation directions of the optical axes 30A of the liquid crystalcompound 30 in the liquid crystal alignment pattern to be opposite toeach other, a reflection direction of circularly polarized light in thepatterned cholesteric liquid crystal layer that reflects rightcircularly polarized light can be made to be the same as that in thepatterned cholesteric liquid crystal layer that reflects left circularlypolarized light.

In addition, this way, in a case where the optical element according tothe embodiment of the present invention includes the patternedcholesteric liquid crystal layers having the same selective reflectioncenter wavelength and different directions of circularly polarized lightto be reflected, it is preferable that the single periods A in theliquid crystal alignment patterns of the patterned cholesteric liquidcrystal layers having the same selective reflection center wavelengthare the same in each in-plane region.

However, the optical element according to the embodiment of the presentinvention is not limited to this configuration and may include acombination of patterned cholesteric liquid crystal layers havingdifferent directions of circularly polarized light to be reflected andincluding an overlapping portion in selective reflection wavelengthranges.

That is, in the optical element according to the embodiment of thepresent invention, even in a case where the selective reflectionwavelength ranges of the two patterned cholesteric liquid crystal layersforming the combination of the patterned cholesteric liquid crystallayers do not completely match each other, as long as at least a part ofthe selective reflection wavelength ranges includes an overlappingportion as shown in FIG. 18 , light having a wavelength in theoverlapping range (hatched area) can be reflected in a large amount oflight.

Here, from the viewpoint of the amount of light reflected in the opticalelement, it is preferable that the patterned cholesteric liquid crystallayers forming the combination of the patterned cholesteric liquidcrystal layers include a wide overlapping range in the selectivereflection wavelength ranges. Specifically, in a case where a rangebetween two wavelengths of a half value transmittance of the patternedcholesteric liquid crystal layers forming the combination of thepatterned cholesteric liquid crystal layers is represented by Δλ_(h), adifference between selective reflection center wavelengths is preferably0.8 × Δλ_(h) nm or less, more preferably 0.6 × Δλ_(h) nm or less, andstill more preferably 0.4 × Δλ_(h) nm or less. In particular, it ispreferable that the selective reflection center wavelengths match eachother, and it is more preferable that the patterned cholesteric liquidcrystal layers have the same selective reflection wavelength range.

In a case where ranges between two wavelengths of a half valuetransmittance of the two patterned cholesteric liquid crystal layers aredifferent, the average value thereof is used as Δλ_(h).

In addition, in the optical element according to the embodiment of thepresent invention, it is preferable that the patterned cholestericliquid crystal layers forming the combination of the patternedcholesteric liquid crystal layers have the same single period A in eachin-plane region. In the present invention, the lengths of the singleperiods A in the liquid crystal alignment patterns being the samerepresents that the difference between the lengths of the single periodsA is 10% or lower.

Here, in respective regions of the patterned cholesteric liquid crystallayers forming the combination of the patterned cholesteric liquidcrystal layers, it is preferable that the difference between the lengthsof the single periods A in the liquid crystal alignment patterns issmall. As described above, the length of the single period A decreases,the reflection angle with respect to incidence light increases.Accordingly, as the difference between the lengths of the single periodsA decreases, directions in which light is reflected from the respectiveregions of the patterned cholesteric liquid crystal layers forming thecombination of the patterned cholesteric liquid crystal layers can bemade similar to each other. In the respective regions of the patternedcholesteric liquid crystal layers forming the combination of thepatterned cholesteric liquid crystal layers, the difference between thelengths of the single periods A in the liquid crystal alignment patternsis preferably 5% or lower and more preferably 3% or lower. It is stillmore preferable that the single periods A match each other.

In addition, in a case where the optical element according to theembodiment of the present invention includes two or more patternedcholesteric liquid crystal layers, it is also preferable that theoptical element includes patterned cholesteric liquid crystal layershaving the same twisted direction of helical structures.

For example, in FIG. 17 , in a patterned cholesteric liquid crystallayer that has a liquid crystal alignment pattern in which a directionof an optical axis derived from a liquid crystal compound rotates in onein-plane direction and that has regions having different pitches ofhelical structures in a plane, optically-anisotropic layers having thesame direction (sense of helical structures) of circularly polarizedlight to be reflected may be laminated and used.

Here, it is preferable that the patterned cholesteric liquid crystallayers have different selective reflection center wavelengths andinclude at least an overlapping portion in selective reflection centerwavelengths.

This way, in a case where the patterned cholesteric liquid crystallayers have different selective reflection center wavelengths and havethe same direction of circularly polarized light to be reflected, theselective reflection wavelength range can be widened.

Here, in the patterned cholesteric liquid crystal layers havingdifferent selective reflection center wavelengths and the same directionof circularly polarized light to be reflected, it is preferable that therotation directions of the optical axes 30A of the liquid crystalcompound 30 in the liquid crystal alignment pattern are the same as eachother.

In the patterned cholesteric liquid crystal layers having differentselective reflection center wavelengths and the same direction ofcircularly polarized light to be reflected, by setting the rotationdirections of the optical axes 30A of the liquid crystal compound 30 inthe liquid crystal alignment pattern to be the same as each other, areflection direction (diffraction direction) of circularly polarizedlight in the patterned cholesteric liquid crystal layer that reflectsright circularly polarized light can be made to be the same as that inanother patterned cholesteric liquid crystal layer that reflects rightcircularly polarized light.

In addition, this way, in a case where the optical element according tothe embodiment of the present invention includes the patternedcholesteric liquid crystal layers having different selective reflectioncenter wavelengths and the same direction of circularly polarized lightto be reflected, it is preferable that the single periods Λ in theliquid crystal alignment patterns of the patterned cholesteric liquidcrystal layers having the same selective reflection center wavelengthare the same. As a result, a diffraction angle with respect to rightcircularly polarized light and a diffraction angle with respect tocircularly polarized light of another layer can be made to be the same.

Method of Forming Regions Having Different Helical Pitches

In the configuration in which the patterned cholesteric liquid crystallayer has regions having different helical pitches, the chiral agent inwhich back isomerization, dimerization, isomerization, dimerization orthe like occurs during light irradiation such that the helical twistingpower (HTP) changes is used. By irradiating the liquid crystalcomposition with light having a wavelength at which the HTP of thechiral agent changes before or during the curing of the liquid crystalcomposition for forming the patterned cholesteric liquid crystal layerwhile changing the irradiation dose for each of the regions, the regionshaving different helical pitches can be formed.

For example, by using a chiral agent in which the HTP decreases duringlight irradiation, the HTP of the chiral agent decreases during lightirradiation. Here, by changing the irradiation dose of light for each ofthe regions, for example, in a region that is irradiated with the lightat a high irradiation dose, the decrease in HTP is large, the inductionof helix is small, and thus the helical pitch increases. On the otherhand, for example, in a region that is irradiated with the light at alow irradiation dose, the decrease in HTP is small, helix is induced bythe original HTP of the chiral agent, and thus the helical pitchdecreases.

The method of changing the irradiation dose of light for each of theregions is not particularly limited, and a method of irradiating lightthrough a gradation mask, a method of changing the irradiation time foreach of the regions, or a method of changing the irradiation intensityfor each of the regions can be used.

The gradation mask refers to a mask in which a transmittance withrespect to light for irradiation changes in a plane.

In all the above-described optical elements according to the embodimentof the present invention, the optical axis 30A of the liquid crystalcompound 30 in the liquid crystal alignment pattern of the patternedcholesteric liquid crystal layer continuously rotates only in the arrowX direction.

However, the present invention is not limited thereto, and variousconfigurations can be used as long as the optical axis 30A of the liquidcrystal compound 30 in the patterned cholesteric liquid crystal layercontinuously rotates in the in-plane direction.

For example, a patterned cholesteric liquid crystal layer 34conceptually shown in a plan view of FIG. 19 can be used, in which aliquid crystal alignment pattern is a concentric circular pattern havinga concentric circular shape where the in-plane direction in which thedirection of the optical axis of the liquid crystal compound 30 changeswhile continuously rotating moves from an inside toward an outside.

Alternatively, a liquid crystal alignment pattern can also be used wherethe in-plane direction in which the direction of the optical axis of theliquid crystal compound 30 changes while continuously rotating isprovided in a radial shape from the center of the patterned cholestericliquid crystal layer 34 instead of a concentric circular shape.

FIG. 19 shows only the liquid crystal compound 30 of the surface of thealignment film as in FIG. 14 . However, as in the example shown in FIG.13 , the patterned cholesteric liquid crystal layer 34 has the helicalstructure in which the liquid crystal compound 30 on the surface of thealignment film is helically turned and laminated as described above.

Further, FIG. 19 shows only one cholesteric liquid crystal layer 34, andthe optical element according to the embodiment of the present inventionmay include the combination of the patterned cholesteric liquid crystallayers as described above. In addition, a preferable configuration andvarious aspects are the same as those of the above-described variousembodiments.

In the patterned cholesteric liquid crystal layer 34 shown in FIG. 19 ,the optical axis (not shown) of the liquid crystal compound 30 is alongitudinal direction of the liquid crystal compound 30.

In the patterned cholesteric liquid crystal layer 34, the direction ofthe optical axis of the liquid crystal compound 30 changes whilecontinuously rotating in a direction in which a large number of opticalaxes move to the outside from the center of the patterned cholestericliquid crystal layer 34, for example, a direction indicated by an arrowA₁, a direction indicated by an arrow A₂, a direction indicated by anarrow A₃, or ....

In addition, as a preferable aspect, for example, the direction of theoptical axis of the liquid crystal compound changes while rotating in aradial direction from the center of the patterned cholesteric liquidcrystal layer 34 as shown in FIG. 19 . In the aspect shown in FIG. 19 ,counterclockwise alignment is shown. The rotation directions of theoptical axes indicated by the respective arrows A1, A2, and A3 in FIG.19 are counterclockwise toward the outside from the center.

In circularly polarized light incident into the patterned cholestericliquid crystal layer 34 having the above-described liquid crystalalignment pattern, the absolute phase changes depending on individuallocal regions having different directions of the optical axes of theliquid crystal compound 30. At this time, the amount of change inabsolute phase varies depending on the directions of the optical axes ofthe liquid crystal compound 30 into which circularly polarized light isincident.

This way, in the patterned cholesteric liquid crystal layer 34 havingthe concentric circular liquid crystal alignment pattern, that is, theliquid crystal alignment pattern in which the optical axis changes whilecontinuously rotating in a radial shape, incidence light can bereflected as diverging light or converging light depending on therotation direction of the optical axis of the liquid crystal compound 30and the direction of circularly polarized light to be reflected.

That is, by setting the liquid crystal alignment pattern of thepatterned cholesteric liquid crystal layer in a concentric circularshape, the optical element according to the embodiment of the presentinvention exhibits, for example, a function as a concave mirror or aconvex mirror.

Here, in a case where the liquid crystal alignment pattern of thepatterned cholesteric liquid crystal layer is concentric circular suchthat the optical element functions as a concave mirror, it is preferablethat the length of the single period Λ over which the optical axisrotates by 180° in the liquid crystal alignment pattern graduallydecreases from the center of the patterned cholesteric liquid crystallayer 34 toward the outer direction in the in-plane direction in whichthe optical axis continuously rotates.

As described above, the reflection angle of light with respect to anincidence direction increases as the length of the single period Λ inthe liquid crystal alignment pattern decreases. Accordingly, the lengthof the single period Λ in the liquid crystal alignment pattern graduallydecreases from the center of the patterned cholesteric liquid crystallayer 34 toward the outer direction in the in-plane direction in whichthe optical axis continuously rotates. As a result, light can be furthergathered, and the performance as a concave mirror can be improved.

Here, as described above, in the patterned cholesteric liquid crystallayer, in a region where the length Λ of the single period in the liquidcrystal alignment pattern is short and the reflection angle is large,the amount of light reflected is small. That is, in the example shown inFIG. 19 , in an outer region where the reflection angle is large, theamount of light reflected is small.

On the other hand, in the optical element according to the embodiment ofthe present invention, the patterned cholesteric liquid crystal layerhas regions having different pitches of helical structures in a plane.In the example shown in FIG. 19 , in the patterned cholesteric liquidcrystal layer 34, the pitch of the helical structure gradually increasesfrom the center toward the outside in the in-plane direction in whichthe optical axis continuously rotates. As a result, a decrease in theamount of light reflected in an outer region of the patternedcholesteric liquid crystal layer 34 can be suppressed.

In the present invention, in a case where the optical element functionsas a convex mirror, it is preferable that the continuous rotationdirection of the optical axis in the liquid crystal alignment pattern isin a direction opposite to that of the case of the above-describedconcave mirror from the center of the patterned cholesteric liquidcrystal layer 34.

In addition, by gradually decreasing the length of the single period Λover which the optical axis rotates by 180° from the center of thepatterned cholesteric liquid crystal layer 34 toward the outer directionin the in-plane direction in which the optical axis continuouslyrotates, light incident into the patterned cholesteric liquid crystallayer can be further diffused, and the performance as a convex mirrorcan be improved.

Further, in the patterned cholesteric liquid crystal layer 34, the pitchof the helical structure gradually increases from the center toward theoutside in the in-plane direction in which the optical axis continuouslyrotates. As a result, a decrease in the amount of light reflected in anouter region of the patterned cholesteric liquid crystal layer 34 can besuppressed.

In the present invention, in a case where the optical element functionsas a convex mirror, it is preferable that a direction of circularlypolarized light to be reflected (sense of a helical structure) from thepatterned cholesteric liquid crystal layer is reversed to be opposite tothat in the case of a concave mirror, that is, the helical twisteddirection of the patterned cholesteric liquid crystal layer is reversed.

Even in this case, by gradually decreasing the length of the singleperiod A over which the optical axis rotates by 180° from the center ofthe patterned cholesteric liquid crystal layer 34 toward the outerdirection in the in-plane direction in which the optical axiscontinuously rotates, light reflected from the patterned cholestericliquid crystal layer can be further diffused, and the performance as aconvex mirror can be improved.

In a state where the helical twisted direction of the patternedcholesteric liquid crystal layer is reversed, it is preferable that thecontinuous rotation direction of the optical axis in the liquid crystalalignment pattern is reversed from the center of the patternedcholesteric liquid crystal layer 34. As a result, the optical elementcan be made to function as a concave mirror.

In the present invention, in a case where the optical element is made tofunction as a convex mirror or a concave mirror, it is preferable thatthe optical element satisfies the following Expression (4).

Φ(r) = (π/λ)[(r² + f²)^(½)- f]

Here, r represents a distance from the center of a concentric circle andis represented by Expression “r = (x² + y²)^(½)”. x and y representin-plane positions, and (x,y) = (0,0) represents the center of theconcentric circle. Φ(r) represents an angle of the optical axis at thedistance r from the center, λ represents the selective reflection centerwavelength of the patterned cholesteric liquid crystal layer, and frepresents a desired focal length.

In the present invention, depending on the uses of the optical element,conversely, the length of the single period Λ in the concentric circularliquid crystal alignment pattern may gradually increase from the centerof the patterned cholesteric liquid crystal layer 34 toward the outerdirection in the in-plane direction in which the optical axiscontinuously rotates.

Further, depending on the uses of the optical element such as a casewhere it is desired to provide a light amount distribution in reflectedlight, a configuration in which regions having partially differentlengths of the single periods Λ in the in-plane direction in which theoptical axis continuously rotates are provided can also be used insteadof the configuration in which the length of the single period Λgradually changes in the in-plane direction in which the optical axiscontinuously rotates.

Further, the optical element according to the embodiment of the presentinvention may include: a patterned cholesteric liquid crystal layer inwhich the single period Λ is uniform over the entire surface; and apatterned cholesteric liquid crystal layer in which regions havingdifferent lengths of the single periods Λ are provided. This point isalso applicable to a configuration in which the optical axiscontinuously rotates only in the in-plane direction as shown in FIG. 12.

FIG. 20 conceptually shows an example of an exposure device that formsthe concentric circular alignment pattern in the alignment film.

An exposure device 80 includes: a light source 84 that includes a laser82; a polarization beam splitter 86 that divides the laser light Memitted from the laser 82 into S polarized light MS and P polarizedlight MP; a mirror 90A that is disposed on an optical path of the Ppolarized light MP; a mirror 90B that is disposed on an optical path ofthe S polarized light MS; a lens 92 that is disposed on the optical pathof the S polarized light MS; a polarization beam splitter 94; and a λ/4plate 96.

The P polarized light MP that is split by the polarization beam splitter86 is reflected from the mirror 90A to be incident into the polarizationbeam splitter 94. On the other hand, the S polarized light MS that issplit by the polarization beam splitter 86 is reflected from the mirror90B and is gathered by the lens 92 to be incident into the polarizationbeam splitter 94.

The P polarized light MP and the S polarized light MS are multiplexed bythe polarization beam splitter 94, are converted into right circularlypolarized light and left circularly polarized light by the λ/4 plate 96depending on the polarization direction, and are incident into thealignment film 24 on the support 20.

Due to interference between the right circularly polarized light and theleft circularly polarized light, the polarization state of light withwhich the alignment film 24 is irradiated periodically changes accordingto interference fringes. The intersection angle between the rightcircularly polarized light and the left circularly polarized lightchanges from the inside to the outside of the concentric circle.Therefore, an exposure pattern in which the pitch changes from theinside to the outside can be obtained. As a result, in the alignmentfilm 24, a concentric circular alignment pattern in which the alignmentstate periodically changes can be obtained.

In the exposure device 80, the length Λ of the single period in theliquid crystal alignment pattern in which the optical axis of the liquidcrystal compound 30 continuously rotates by 180° can be controlled bychanging the refractive power of the lens 92 (the F number of the lens92), the focal length of the lens 92, the distance between the lens 92and the alignment film 24, and the like.

In addition, by adjusting the refractive power of the lens 92 (the Fnumber of the lens 92), the length Λ of the single period in the liquidcrystal alignment pattern in the in-plane direction in which the opticalaxis continuously rotates can be changed. Specifically, In addition, thelength Λ of the single period in the liquid crystal alignment pattern inthe in-plane direction in which the optical axis continuously rotatescan be changed depending on a light spread angle at which light isspread by the lens 92 due to interference with parallel light. Morespecifically, in a case where the refractive power of the lens 92 isweak, light is approximated to parallel light. Therefore, the length Λof the single period in the liquid crystal alignment pattern graduallydecreases from the inside toward the outside, and the F numberincreases. Conversely, in a case where the refractive power of the lens92 becomes stronger, the length A of the single period in the liquidcrystal alignment pattern rapidly decreases from the inside toward theoutside, and the F number decreases.

This way, the configuration of changing the length of the single periodΛ over which the optical axis rotates by 180° in the in-plane directionin which the optical axis continuously rotates can also be used in theconfiguration shown in FIGS. 13, 14, and 15 in which the optical axis30A of the liquid crystal compound 30 changes while continuouslyrotating only in the in-plane direction as the arrow X direction.

For example, by gradually decreasing the single period Λ of the liquidcrystal alignment pattern in the arrow X direction, an optical elementthat reflects light to be gathered can be obtained.

In addition, by reversing the direction in which the optical axis in theliquid crystal alignment pattern rotates by 180°, an optical elementthat reflects light to be diffused only in the arrow X direction can beobtained. Likewise, by reversing the direction of circularly polarizedlight to be reflected (sense of a helical structure) from thecholesteric liquid crystal layer, an optical element that reflects lightto be diffused only in the arrow X direction can be obtained. Byreversing the direction (the sense of the helical structure) in whichthe optical axis of the liquid crystal alignment pattern rotates by 180°in a state where the direction of circularly polarized light to bereflected from the cholesteric liquid crystal layer, an optical elementthat reflects light to be gathered can be obtained.

Further, depending on the uses of the optical element such as a casewhere it is desired to provide a light amount distribution in reflectedlight, a configuration in which regions having partially differentlengths of the single periods Λ in the arrow X direction are providedcan also be used instead of the configuration in which the length of thesingle period Λ gradually changes in the arrow X direction. For example,as a method of partially changing the single period Λ, for example, amethod of scanning and exposing the photo-alignment film to be patternedwhile freely changing a polarization direction of laser light to begathered can be used.

The optical element according to the embodiment of the present inventioncan be used for various uses where light is reflected at an angle otherthan the angle of specular reflection, for example, an optical pathchanging member, a light gathering element, a light diffusing element toa predetermined direction, a diffraction element, or the like in anoptical device.

In the above-described example, the optical element according to theembodiment of the present invention is used as the optical element thatreflects visible light. However, the present invention is not limited tothis example, and various configurations can be used.

For example, the optical element according to the embodiment of thepresent invention also may be configured to reflect infrared light orultraviolet light or to reflect only light other than visible light.

Hereinabove, the optical element according to the second aspect of thepresent invention has been described above. However, the presentinvention is not limited to the above-described examples, and variousimprovements and modifications can be made within a range not departingfrom the scope of the present invention.

EXAMPLES

Hereinafter, the characteristics of the first aspect of the presentinvention will be described in detail using examples. Materials,chemicals, used amounts, material amounts, ratios, treatment details,treatment procedures, and the like shown in the following examples canbe appropriately changed within a range not departing from the scope ofthe present invention. Accordingly, the scope of the present inventionis not limited to the following specific examples.

Comparative Example 1-1 Formation of Alignment Film

The following alignment film-forming coating solution was applied to aglass substrate by spin coating. The support on which the coating filmof the alignment film-forming coating solution was formed was driedusing a hot plate at 60° C. for 60 seconds. As a result, an alignmentfilm was formed.

Alignment Film-Forming Coating Solution The following material forphoto-alignment... 1.00 part by mass Water ... 16.00 parts by massButoxyethanol ... 42.00 parts by mass Propylene glycol monomethyl ether... 42.00 parts by mass

Material for Photo-Alignment

Exposure of Alignment Film

By using the exposure device shown in FIG. 4 as the exposure device forexposing the alignment film, the alignment film was exposed to form analignment film P-1 having an alignment pattern.

In the exposure device, a laser that emits laser light having awavelength (325 nm) was used as the laser. The exposure dose of theinterference light was 300 mJ/cm². The single period (the length overwhich the optical axis rotates by 180°) of an alignment pattern formedby interference of two laser beams was controlled to be 0.41 µm bychanging an intersection angle (intersection angle α) between the twobeams.

Formation of Cholesteric Liquid Crystal Layer

As the liquid crystal composition forming the cholesteric liquid crystallayer, the following composition A-1 was prepared. This composition A-1is a liquid crystal composition forming a cholesteric liquid crystallayer (cholesteric liquid crystalline phase) that reflects rightcircularly polarized light.

Composition A-1 Rod-shaped liquid crystal compound L-1 ...  100.00 partsby mass Polymerization initiator (IRGACURE (registered trade name) 907,manufactured by BASF SE) ...  3.00 parts by mass Photosensitizer(KAYACURE DETX-S, manufactured by Nippon Kayaku Co., Ltd.) ...  1.00part by mass Chiral agent Ch-1  ...  4.00 parts by mass Chiral agentCh-2A  ...  1.00 part by mass Leveling agent T-1  ...  0.08 parts bymass Methyl ethyl ketone  ...  2660.00 parts by mass

Rod-Shaped Liquid Crystal Compound L-1

Chiral Agent Ch-1

Chiral Agent Ch-2A

Leveling Agent T-1

The cholesteric liquid crystal layer was formed by applying multiplelayers of the composition A-1 to the alignment film P-1. The applicationof the multiple layers refers to repetition of the following processesincluding: preparing a first liquid crystal immobilized layer byapplying the first layer-forming composition A-1 to the alignment film,heating the composition A-1, cooling the composition A-1, andirradiating the composition A-1 with ultraviolet light for curing; andpreparing a second or subsequent liquid crystal immobilized layer byapplying the second or subsequent layer-forming composition A-1 to theformed liquid crystal immobilized layer, heating the composition A-1,cooling the composition A-1, and irradiating the composition A-1 withultraviolet light for curing as described above. Even in a case wherethe liquid crystal layer was formed by the application of the multiplelayers such that the total thickness of the liquid crystal layer waslarge, the alignment direction of the alignment film was reflected froma lower surface of the cholesteric liquid crystal layer to an uppersurface thereof.

Regarding the first liquid crystal layer, the composition A-1 wasapplied to the alignment film P-1 to form a coating film, the coatingfilm was heated using a hot plate at 95° C., the coating film was cooledto 80° C., and the coating film was irradiated with ultraviolet lighthaving a wavelength of 365 nm at an irradiation dose of 300 mJ/cm² usinga high-pressure mercury lamp in a nitrogen atmosphere. As a result, thealignment of the liquid crystal compound was immobilized. At this time,the thickness of the first liquid crystal layer was 0.2 µm.

Regarding the second or subsequent liquid crystal layer, the compositionwas applied to the first liquid crystal layer, and the appliedcomposition was heated, cooled, and irradiated with ultraviolet lightfor curing under the same conditions as described above. As a result, aliquid crystal immobilized layer was prepared. This way, by repeatingthe application multiple times until the total thickness reached adesired thickness, and a cholesteric liquid crystal layer was formed.

In a case where a cross-section of the cholesteric liquid crystal layerwas observed with a scanning electron microscope (SEM), the cholestericliquid crystalline phase of the cholesteric liquid crystal layer had 2pitches. In addition, a slope pitch of tilted surfaces of brightportions and dark portions with respect to a main surface (an intervalbetween bright portions or between dark portions in the normal directionwith respect to the slope was set as ½ surface pitch) was 0.42 µm. Apitch of tilted surfaces of bright portions and dark portions in a SEMcross-section of the cholesteric liquid crystal layer changes dependingon the helical pitch of the cholesteric liquid crystalline phase and thesingle period of the liquid crystal alignment pattern.

It was verified using a polarizing microscope that the cholestericliquid crystal layer had a periodic alignment pattern as shown in FIG. 2.

The selective reflection center wavelength of the cholesteric liquidcrystal layer was measured using a spectrophotometer (manufactured byShimadzu Corporation, UV-3150).

Example 1-1 Formation of Patterned Cholesteric Liquid Crystal Layer

As the liquid crystal composition forming the cholesteric liquid crystallayer, the following composition A-2A was prepared. This compositionA-2A is a liquid crystal composition forming a cholesteric liquidcrystal layer (cholesteric liquid crystalline phase) that reflects rightcircularly polarized light.

Composition A-2A Rod-shaped liquid crystal compound L-1 ... 100.00 partsby mass Polymerization initiator (IRGACURE (registered trade name) 907,manufactured by BASF SE) ... 3.00 parts by mass Photosensitizer(KAYACURE DETX-S, manufactured by Nippon Kayaku Co., Ltd.) ... 1.00 partby mass Chiral agent Ch-1 ... 4.00 parts by mass Chiral agent Ch-2A ...1.00 part by mass Leveling agent T-1 ... 0.08 parts by mass Methyl ethylketone ... 2660.00 parts by mass

The patterned cholesteric liquid crystal layer was formed by applyingmultiple layers of the composition A-2A to the alignment film P-1. Theapplication of the multiple layers refers to repetition of the followingprocesses including: preparing a first liquid crystal immobilized layerby applying the first layer-forming composition A-2A to the alignmentfilm, heating the composition A-2A, cooling the composition A-2A, andirradiating the composition A-2A with ultraviolet light for curing; andpreparing a second or subsequent liquid crystal immobilized layer byapplying the second or subsequent layer-forming composition A-2A to theformed liquid crystal immobilized layer, heating the composition A-2A,cooling the composition A-2A, and irradiating the composition A-2A withultraviolet light for curing as described above. Even in a case wherethe liquid crystal layer was formed by the application of the multiplelayers such that the total thickness of the liquid crystal layer waslarge, the alignment direction of the alignment film was reflected froma lower surface of the liquid crystal layer to an upper surface thereof.

First, regarding the first liquid crystal layer, the composition A-2Awas applied to the alignment film P-1, and the coating film was heatedon a hot plate at 95° C. Next, the coating film was cooled to 25° C. andwas irradiated with ultraviolet light using a high-pressure mercurylamp. At this time, the irradiation was performed through a long passfilter cutting a wavelength of 350 nm or less. At this time, the coatingfilm was irradiated while changing the irradiation dose of ultravioletlight in a plane. Specifically, the coating film was irradiated whilegradually changing the irradiation dose in the in-plane direction inwhich the optical axis rotated such that the irradiation dose of one endportion was 0 mJ/cm² and the irradiation dose of another end portion was10 mJ/cm². Next, the coating film was heated again to 95° C. on a hotplate, was cooled to 80° C., and was irradiated with ultraviolet lightusing a high-pressure mercury lamp under a nitrogen atmosphere. As aresult, the alignment of the liquid crystal compound was immobilized. Atthis time, the thickness of the first liquid crystal layer was 0.2 µm.

Regarding the second or subsequent liquid crystal layer, the compositionwas applied to the first liquid crystal layer, and then a liquid crystalimmobilized layer was prepared under the same conditions as describedabove. This way, by repeating the application multiple times until thetotal thickness reached a desired thickness, and a patterned cholestericliquid crystal layer was formed.

In a case where a cross-section of the patterned cholesteric liquidcrystal layer was observed with a scanning electron microscope (SEM),the cholesteric liquid crystalline phase of the reflecting layer had 2pitches. In addition, it was found that the slope pitch of tiltedsurfaces of bright portions and dark portions with respect to a mainsurface changed in a range of 0.37 µm to 0.41 µm.

It was verified using a polarizing microscope that the patternedcholesteric liquid crystal layer had a periodic alignment pattern asshown in FIG. 2 .

Example 1-2

A patterned cholesteric liquid crystal layer was formed using the samemethod as that of Example 1-1, except that the single period (the lengthover which the optical axis rotated by 180°) of the alignment pattern ofthe alignment film was controlled to be 0.34 µm by changing theintersection angle α and the addition amount of the chiral agent Ch-1 inthe composition for forming the patterned cholesteric liquid crystallayer was changed to 5.60 parts by mass.

In a case where a cross-section of the patterned cholesteric liquidcrystal layer was observed with a scanning electron microscope (SEM),the cholesteric liquid crystalline phase of the patterned cholestericliquid crystal layer had 2 pitches. In addition, it was found that theslope pitch of tilted surfaces of bright portions and dark portions withrespect to a main surface changed in a range of 0.31 µm to 0.36 µm.

It was verified using a polarizing microscope that the patternedcholesteric liquid crystal layer had a periodic alignment pattern asshown in FIG. 2 .

Comparative Example 1-2

A cholesteric liquid crystal layer was formed using the same method asthat of Comparative Example 1-1, except that the single period (thelength over which the optical axis rotated by 180°) of the alignmentpattern of the alignment film was controlled to be 0.34 µm by changingthe intersection angle α and the addition amount of the chiral agentCh-1 in the composition for forming the cholesteric liquid crystal layerwas changed to 5.60 parts by mass.

In a case where a cross-section of the cholesteric liquid crystal layerwas observed with a scanning electron microscope (SEM), the cholestericliquid crystalline phase of the cholesteric liquid crystal layer had 2pitches. In addition, the slope pitch of tilted surfaces of brightportions and dark portions with respect to a main surface was 0.36 µm.

It was verified using a polarizing microscope that the cholestericliquid crystal layer had a periodic alignment pattern as shown in FIG. 2.

Example 1-3

A patterned cholesteric liquid crystal layer was formed using the samemethod as that of Example 1-1, except that the single period (the lengthover which the optical axis rotated by 180°) of the alignment pattern ofthe alignment film was controlled to be 0.49 µm by changing theintersection angle α and the addition amount of the chiral agent Ch-1 inthe composition for forming the patterned cholesteric liquid crystallayer was changed to 3.20 parts by mass.

In a case where a cross-section of the patterned cholesteric liquidcrystal layer was observed with a scanning electron microscope (SEM),the cholesteric liquid crystalline phase of the patterned cholestericliquid crystal layer had 2 pitches. In addition, it was found that theslope pitch of tilted surfaces of bright portions and dark portions withrespect to a main surface changed in a range of 0.43 µm to 0.48 µm.

It was verified using a polarizing microscope that the patternedcholesteric liquid crystal layer had a periodic alignment pattern asshown in FIG. 2 .

Comparative Example 1-3

A cholesteric liquid crystal layer was formed using the same method asthat of Comparative Example 1-1, except that the single period (thelength over which the optical axis rotated by 180°) of the alignmentpattern of the alignment film was controlled to be 0.49 µm by changingthe intersection angle α and the addition amount of the chiral agentCh-1 in the composition for forming the cholesteric liquid crystal layerwas changed to 3.2 parts by mass.

In a case where a cross-section of the cholesteric liquid crystal layerwas observed with a scanning electron microscope (SEM), the cholestericliquid crystalline phase of the cholesteric liquid crystal layer had 2pitches. In addition, the slope pitch of tilted surfaces of brightportions and dark portions with respect to a main surface was 0.50 µm.

It was verified using a polarizing microscope that the cholestericliquid crystal layer had a periodic alignment pattern as shown in FIG. 2.

Evaluation Emitted Light Intensity Distribution (Uniformity)

As shown in FIG. 10 , each of the optical elements according to Examplesand Comparative Examples prepared as described above was disposed on asurface of the light guide plate 44 to prepare a light guide element. InFIG. 10 , the optical element was disposed on a surface (position ofDOE-2) of an end portion of the light guide plate on an emission side.In addition, the optical element of which the thickness was adjustedsuch that the cholesteric liquid crystalline phase had 8 pitches in theoptical element according to the corresponding Comparative Example wasdisposed on a surface (position of DOE-1) of an end portion of the lightguide plate 44 on an incidence side.

As the light guide plate 44, a glass light guide plate having arefractive index of 1.52 and a thickness of 1 mm was used.

In addition, the optical element and the light guide plate 44 werebonded to each other using a heat-sensitive adhesive.

In addition, the optical element of DOE-1 and the optical element ofDOE-2 were disposed such that directions of in-plane periods of theliquid crystal alignment patterns were opposite to each other.

As shown in FIG. 10 , in the end portion of the light guide plate 44 onthe side where DOE-1 was disposed, a laser was disposed to face asurface opposite to the surface where DOE-1 was disposed such that alinear polarizer 100 and an λ/4 plate 102 were disposed between thelaser and the light guide plate 44.

On the other hand, in the end portion of the light guide plate 44 on theside where DOE-2 was disposed, a light screen 104 was disposed to face asurface opposite to the surface where DOE-2 was disposed. In the lightscreen 104, a pinhole 104 a having a diameter of 2 mm was formed.

In a case where light is emitted from the laser, the light passedthrough the linear polarizer 100 and the λ/4 plate 102 to be convertedinto right circularly polarized light, and the right circularlypolarized light was incident into the light guide plate 44. The lightincident into the light guide plate 44 was incident into the opticalelement of DOE-1.

The diffracted light that was reflected and diffracted due to thediffraction effect and the selective reflection effect of the opticalelement of DOE-1 propagated in the light guide plate 44. The lightpropagated in the light guide plate 44 was diffracted and reflected inthe optical element of DOE-2 to be emitted in the direction of the lightscreen 104.

The intensity (emitted light intensity) of the light emitted from thelight guide plate 44 was measured through the pinhole 104 a of the lightscreen 104. By changing the position of the pinhole 104 a, the emittedlight intensity was measured at each position of the optical element ofDOE-2. The emitted light intensity was measured using a Power Meter1918-C (manufactured by Newport Corporation).

For Example 1-1 and Comparative Example 1-1, the measurement wasperformed using a laser that emits light having a wavelength of 532 nm.For Example 1-2 and Comparative Example 1-2, the measurement wasperformed using a laser that emits light having a wavelength of 450 nm.For Example 1-3 and Comparative Example 1-3, the measurement wasperformed using a laser that emits light having a wavelength of 635 nm.

A ratio of a minimum value to a maximum value of the measured emittedlight intensity was obtained to evaluate uniformity based on thefollowing standards.

-   A: the ratio (minimum value/maximum value) of the minimum value to    the maximum value of the emitted light intensity was 0.8 or higher-   B: the ratio (minimum value/maximum value) of the minimum value to    the maximum value of the emitted light intensity was 0.7 or higher    and lower than 0.8-   C: the ratio (minimum value/maximum value) of the minimum value to    the maximum value of the emitted light intensity was 0.5 or higher    and lower than 0.7-   D: the ratio (minimum value/maximum value) of the minimum value to    the maximum value of the emitted light intensity was lower than 0.5

The results are shown in Table 1.

TABLE 1 Comparative Example 1-1 Example 1-1 Comparative Example 1-2Example 1-2 Comparative Example 1-3 Example 1-3 Cholesteric LiquidCrystal Layer (Incidence Side) In-Plane Period [µm] 0.41 0.41 0.34 0.340.49 0.49 Slope Pitch [µm] 0.42 0.42 0.36 0.36 0.50 0.50 CholestericLiquid Crystal Layer (Emission Side) In-Plane Period [µm] 0.41 0.41 0.340.34 0.49 0.49 Slope Pitch [µm] 0.42 Change 0.36 Change 0.50 ChangeEvaluation Uniformity D A D A D A

As shown in Table 1, regarding Examples of the optical element accordingto the embodiment of the present invention in which the patternedcholesteric liquid crystal layer has a liquid crystal alignment patternin which a direction of an optical axis derived from a liquid crystalcompound changes while continuously rotating in at least one in-planedirection and the cholesteric liquid crystal layer has regions havingdifferent pitches of helical structures in a plane, it can be seen that,in a case where the optical element is used as a diffraction element ofa light guide element on an emission side, the emitted light intensityis constant irrespective of positions such that uniform light was ableto be emitted.

Example 1-4

A first patterned cholesteric liquid crystal layer was formed using thesame method as that of Example 1-1, except that the addition amount ofthe chiral agent Ch-1 in the composition A-2A was changed to 4.26 partsby mass.

In a case where a cross-section of the first patterned cholestericliquid crystal layer was observed with a scanning electron microscope(SEM), the cholesteric liquid crystalline phase of the reflecting layerhad 2 pitches. In addition, it was found that the slope pitch of tiltedsurfaces of bright portions and dark portions with respect to a mainsurface changed in a range of 0.35 µm to 0.39 µm.

The in-plane period of the first patterned cholesteric liquid crystallayer was 0.41 µm.

A second patterned cholesteric liquid crystal layer was formed on thefirst patterned cholesteric liquid crystal layer using the same methodas that of Example 1-1, except that the addition amount of the chiralagent Ch-1 in the composition A-2A was changed to 3.65 parts by mass.

In a case where a cross-section of the second patterned cholestericliquid crystal layer was observed with a scanning electron microscope(SEM), the cholesteric liquid crystalline phase of the reflecting layerhad 2 pitches. In addition, it was found that the slope pitch of tiltedsurfaces of bright portions and dark portions with respect to a mainsurface changed in a range of 0.4 µm to 0.44 µm.

The in-plane period of the second patterned cholesteric liquid crystallayer was 0.41 µm.

A light guide element in which the second patterned cholesteric liquidcrystal layer was laminated on the first patterned cholesteric liquidcrystal layer was used as DOE-2.

The following optical element was prepared as the optical element(DOE-1) on the incidence side.

A first cholesteric liquid crystal layer was formed using the samepreparation method as that of the cholesteric liquid crystal layeraccording to Comparative Example 1-1, except that the addition amount ofthe chiral agent Ch-1 in the composition A-1 was changed to 4.26 partsby mass.

In a case where a cross-section of the first cholesteric liquid crystallayer was observed with a scanning electron microscope (SEM), thecholesteric liquid crystalline phase of the first cholesteric liquidcrystal layer had 8 pitches. In addition, the slope pitch of tiltedsurfaces of bright portions and dark portions with respect to a mainsurface was 0.39 µm.

The single period of the in-plane alignment pattern of the firstcholesteric liquid crystal layer was 0.41 µm.

A second cholesteric liquid crystal layer was formed on the firstcholesteric liquid crystal layer using the same preparation method asthat of the cholesteric liquid crystal layer according to ComparativeExample 1-1, except that the addition amount of the chiral agent Ch-1 inthe composition A-1 was changed to 3.65 parts by mass.

In a case where a cross-section of the second cholesteric liquid crystallayer was observed with a scanning electron microscope (SEM), thecholesteric liquid crystalline phase of the second cholesteric liquidcrystal layer had 8 pitches. In addition, the slope pitch of tiltedsurfaces of bright portions and dark portions with respect to a mainsurface was 0.44 µm.

The period of the in-plane alignment pattern of the second cholestericliquid crystal layer was 0.41 µm.

A light guide element in which the second cholesteric liquid crystallayer was laminated on the first cholesteric liquid crystal layer wasused as DOE-1.

Evaluation

Using the same method as that of Example 1-1, the optical elementprepared as described above was disposed on a surface of the light guideplate 44 to prepare a light guide element. A light guide elementaccording to Example 1-5 was prepared using the same preparation methodas that of the light guide element according to Example 1-1, except thatthe optical element on the incidence side was changed to the opticalelement on the incidence side prepared in Example 1-4.

As shown in FIG. 10 , in the end portion of the light guide plate 44 onthe side where DOE-1 was disposed, a laser was disposed to face asurface opposite to the surface where DOE-1 was disposed such that alinear polarizer 100 and an λ/4 plate 102 were disposed between thelaser and the light guide plate 44.

On the other hand, in the end portion of the light guide plate 44 on theside where DOE-2 was disposed, a light screen 104 was disposed to face asurface opposite to the surface where DOE-2 was disposed. In the lightscreen 104, a pinhole 104 a having a diameter of 2 mm was formed.

While changing the angle of the incidence light from the laser in FIG.10 at an interval of 5° in a range of -20° to +20°, the intensity(emitted light intensity) of the light emitted from the light guideplate 44 was measured through the pinhole 104 a of the light screen 104.By changing the position of the pinhole 104 a, the emitted lightintensity was measured at each position of the optical element of DOE-2.The emitted light intensity was measured using a Power Meter 1918-C(manufactured by Newport Corporation).

For Example 1-4 and Example 1-5, the measurement was performed using alaser that emits light having a wavelength of 532 nm.

As a result of a comparison between Examples 1-4 and 1-5, the incidenceangle range having a high diffraction efficiency (high emitted lightintensity) in Example 1-4 was wider than that in Example 1-5.

As described above, regarding the optical element according to theembodiment of the present invention including a plurality of cholestericliquid crystal layers having the same twisted direction of the helicalstructure and having different slope pitches, in which the cholestericliquid crystal layer has a liquid crystal alignment pattern in which adirection of an optical axis derived from a liquid crystal compoundchanges while continuously rotating in at least one in-plane direction,and the cholesteric liquid crystal layer has regions having differentpitches of helical structures in a plane, it can be seen that, in a casewhere the optical element is used as a diffraction element of a lightguide element on an emission side, the incidence angle range having ahigh diffraction efficiency can be widened. In a case where this lightguide element is used for AR glasses, light can be efficiently reflectedwith a wide viewing angle range, and a bright display can be obtained.

Hereinafter, the characteristics of the second aspect of the presentinvention will be described in detail using examples. Materials,chemicals, used amounts, material amounts, ratios, treatment details,treatment procedures, and the like shown in the following examples canbe appropriately changed within a range not departing from the scope ofthe present invention. Accordingly, the scope of the present inventionis not limited to the following specific examples.

Comparative Example 2-1 Preparation of First Reflecting Layer Supportand Saponification Treatment of Support

As the support, a commercially available triacetyl cellulose film(manufactured by Fujifilm Corporation, Z-TAC) was used.

The support was caused to pass through an induction heating roll at atemperature of 60° C. such that the support surface temperature wasincreased to 40° C.

Next, an alkali solution shown below was applied to a single surface ofthe support using a bar coater in an application amount of 14 mL(liter)/m², the support was heated to 110° C., and the support wastransported for 10 seconds under a steam infrared electric heater(manufactured by Noritake Co., Ltd.).

Next, 3 mL/m² of pure water was applied to a surface of the support towhich the alkali solution was applied using the same bar coater. Next,water cleaning using a foundry coater and water draining using an airknife were repeated three times, and then the support was transportedand dried in a drying zone at 70° C. for 10 seconds. As a result, thealkali saponification treatment was performed on the surface of thesupport.

Alkali Solution Potassium hydroxide  ...  4.70 parts by mass Water ... 15.80 parts by mass Isopropanol  ...  63.70 parts by mass SurfactantSF-1: C₁₄H₂₉O(CH₂CH₂O)₂OH ...  1.0 part by mass Propylene glycol... 14.8 parts by mass

Formation of Undercoat Layer

The following undercoat layer-forming coating solution was continuouslyapplied to the surface of the support on which the alkali saponificationtreatment was performed using a #8 wire bar. The support on which thecoating film was formed was dried using warm air at 60° C. for 60seconds and was dried using warm air at 100° C. for 120 seconds. As aresult, an undercoat layer was formed.

Undercoat Layer-Forming Coating Solution The following modifiedpolyvinyl alcohol ...  2.40 parts by mass Isopropyl alcohol  ...  1.60parts by mass Methanol  ...  36.00 parts by mass Water ...  60.00 partsby mass

Modified Polyvinyl Alcohol

Formation of Alignment Film

The following alignment film-forming coating solution was continuouslyapplied to the support on which the undercoat layer was formed using a#2 wire bar. The support on which the coating film of the alignmentfilm-forming coating solution was formed was dried using a hot plate at60° C. for 60 seconds. As a result, an alignment film was formed.

Alignment Film-Forming Coating Solution The following material forphoto-alignment...  1.00 part by mass Water  ...  16.00 parts by massButoxyethanol ...  42.00 parts by mass Propylene glycol monomethylether  ...  42.00 parts by mass

-Material for Photo-Alignment-

Exposure of Alignment Film

By using the exposure device shown in FIG. 20 as the exposure device forexposing the alignment film, the alignment film P-1 was formed. By usingthe exposure device shown in FIG. 20 , the single period of thealignment pattern gradually decreased toward the outer direction.

Formation of Cholesteric Liquid Crystal Layer

As the liquid crystal composition forming the cholesteric liquid crystallayer, the following composition A-1 was prepared. This composition A-1is a liquid crystal composition forming a cholesteric liquid crystallayer (cholesteric liquid crystalline phase) that has a selectivereflection center wavelength of 650 nm and reflects right circularlypolarized light.

Composition A-1 Rod-shaped liquid crystal compound L-1 ...  100.00 partsby mass Polymerization initiator (IRGACURE (registered trade name) 907,manufactured by BASF SE)  ...  3.00 parts by mass Photosensitizer(KAYACURE DETX-S, manufactured by Nippon Kayaku Co., Ltd.) ...  1.00part by mass Chiral agent Ch-1  ...  4.57 parts by mass Leveling agentT-1  ...  0.08 parts by mass Methyl ethyl ketone  ...  977.00 parts bymass

p Chiral Agent Ch-1

The cholesteric liquid crystal layer was formed by applying multiplelayers of the composition A-1 to the alignment film P-1. The applicationof the multiple layers refers to repetition of the following processesincluding: preparing a first liquid crystal immobilized layer byapplying the first layer-forming composition A-1 to the alignment film,heating the composition A-1, cooling the composition A-1, andirradiating the composition A-1 with ultraviolet light for curing; andpreparing a second or subsequent liquid crystal immobilized layer byapplying the second or subsequent layer-forming composition A-1 to theformed liquid crystal immobilized layer, heating the composition A-1,cooling the composition A-1, and irradiating the composition A-1 withultraviolet light for curing as described above. Even in a case wherethe liquid crystal layer was formed by the application of the multiplelayers such that the total thickness of the liquid crystal layer waslarge, the alignment direction of the alignment film was reflected froma lower surface of the liquid crystal layer to an upper surface thereof.

Regarding the first liquid crystal layer, the composition A-1 wasapplied to the alignment film P-1 to form a coating film, the coatingfilm was heated using a hot plate at 95° C., the coating film was cooledto 25° C., and the coating film was irradiated with ultraviolet lighthaving a wavelength of 365 nm at an irradiation dose of 100 mJ/cm² usinga high-pressure mercury lamp in a nitrogen atmosphere. As a result, thealignment of the liquid crystal compound was immobilized. At this time,the thickness of the first liquid crystal layer was 0.2 µm.

Regarding the second or subsequent liquid crystal layer, the compositionwas applied to the first liquid crystal layer, and the appliedcomposition was heated, cooled, and irradiated with ultraviolet lightfor curing under the same conditions as described above. As a result, aliquid crystal immobilized layer was prepared. This way, by repeatingthe application multiple times until the total thickness reached adesired thickness, and a cholesteric liquid crystal layer was formed.

In a case where a cross-section of the cholesteric liquid crystal layerwas observed with a scanning electron microscope (SEM), the cholestericliquid crystalline phase of the cholesteric liquid crystal layer had 8pitches.

It was verified using a polarizing microscope that the cholestericliquid crystal layer had a periodically aligned surface having aconcentric circular shape (radial shape) as shown in FIG. 19 . In theliquid crystal alignment pattern of the cholesteric liquid crystallayer, regarding the single period over which the optical axis of theliquid crystal compound rotated by 180°, the single period of a centerportion was 181 µm, the single period of a portion at a distance of 5 mmfrom the center was 1.8 µm, the single period of a portion at a distanceof 10 mm from the center was 1.0 µm. This way, the single perioddecreased toward the outer direction.

In addition, the selective reflection center wavelengths of thecholesteric liquid crystal layer were 650 nm at the center portion, atthe position at a distance of 5 mm from the center, and at the positionat a distance of 10 mm from the center. That is, the pitch of thehelical structure of the cholesteric liquid crystal layer was uniform ina plane.

The selective reflection center wavelength of the cholesteric liquidcrystal layer was measured using a spectrophotometer (manufactured byShimadzu Corporation, UV-3150).

Example 2-1 Formation of Patterned Cholesteric Liquid Crystal Layer

As the liquid crystal composition forming the patterned cholestericliquid crystal layer, the following composition A-2A was prepared. Thiscomposition A-2A is a liquid crystal composition forming a patternedcholesteric liquid crystal layer (cholesteric liquid crystalline phase)that reflects right circularly polarized light.

Composition A-2A Rod-shaped liquid crystal compound L-1 ... 100.00 partsby mass Polymerization initiator (IRGACURE (registered trade name) 907,manufactured by BASF SE) ... 3.00 parts by mass Chiral agent Ch-2A ...3.84 part by mass Leveling agent T-1 ... 0.08 parts by mass Methyl ethylketone ... 977.00 parts by mass

Chiral Agent Ch-2A

The patterned cholesteric liquid crystal layer was formed by applyingmultiple layers of the composition A-2A to the alignment film P-1. Theapplication of the multiple layers refers to repetition of the followingprocesses including: preparing a first liquid crystal immobilized layerby applying the first layer-forming composition A-2A to the alignmentfilm, heating the composition A-2A, cooling the composition A-2A, andirradiating the composition A-2A with ultraviolet light for curing; andpreparing a second or subsequent liquid crystal immobilized layer byapplying the second or subsequent layer-forming composition A-2A to theformed liquid crystal immobilized layer, heating the composition A-2A,cooling the composition A-2A, and irradiating the composition A-2A withultraviolet light for curing as described above. Even in a case wherethe liquid crystal layer was formed by the application of the multiplelayers such that the total thickness of the liquid crystal layer waslarge, the alignment direction of the alignment film was reflected froma lower surface of the liquid crystal layer to an upper surface thereof.

First, in order to form the first layer, the composition A-2A wasapplied to the alignment film P-1, and the coating film was heated on ahot plate at 95° C. Next, the coating film was cooled to 25° C. and wasirradiated with only ultraviolet light (i-ray) having a wavelength of365 nm using a LED light source under a nitrogen atmosphere. At thistime, the coating film was irradiated while changing the irradiationdose of ultraviolet light in a plane. Specifically, the coating film wasirradiated while changing the irradiation dose to 0 mJ/cm² (centerportion), 30 mJ/cm² (the distance of 5 mm from the center), and 60mJ/cm² (the distance of 10 mm from the center) in a plane. Next, thecoating film was heated to 95° C. on a hot plate, was cooled to 25° C.,and was irradiated with mixed ultraviolet light having a wavelength of350 nm or shorter using a high-pressure mercury lamp under a nitrogenatmosphere. As a result, the alignment of the liquid crystal compoundwas immobilized. At this time, the thickness of the first liquid crystallayer was 0.2 µm.

Regarding the second or subsequent liquid crystal layer, the compositionwas applied to the first liquid crystal layer, and then a liquid crystalimmobilized layer was prepared under the same conditions as describedabove. This way, by repeating the application multiple times until thetotal thickness reached a desired thickness, and a patterned cholestericliquid crystal layer was formed.

In a case where a cross-section of the patterned cholesteric liquidcrystal layer was observed with a scanning electron microscope (SEM),the cholesteric liquid crystalline phase of the patterned cholestericliquid crystal layer had 8 pitches.

It was verified using a polarizing microscope that the patternedcholesteric liquid crystal layer had a periodically aligned surfacehaving a concentric circular shape (radial shape) as shown in FIG. 19 .In the liquid crystal alignment pattern of the patterned cholestericliquid crystal layer, regarding the single period over which the opticalaxis of the liquid crystal compound rotated by 180°, the single periodof a center portion was 181 µm, the single period of a portion at adistance of 5 mm from the center was 1.8 µm, the single period of aportion at a distance of 10 mm from the center was 1.0 µm. This way, thesingle period decreased toward the outer direction. In addition, theselective reflection center wavelengths of the patterned cholestericliquid crystal layer were 650 nm at the center portion, 700 nm at theposition at a distance of 5 mm from the center, and 750 nm at theposition at a distance of 10 mm from the center. That is, the pitch ofthe helical structure of the cholesteric liquid crystal layer increasedtoward the outside.

Example 2-2

A patterned cholesteric liquid crystal layer was formed using the samemethod as that of Example 2-1, except that the chiral agent Ch-2A waschanged to a chiral agent Ch-2B having the following structure and theaddition amount thereof was changed to 3.85 parts by mass.

Chiral Agent Ch-2B

In a case where a cross-section of the patterned cholesteric liquidcrystal layer was observed with a scanning electron microscope (SEM),the cholesteric liquid crystalline phase of the patterned cholestericliquid crystal layer had 8 pitches.

It was verified using a polarizing microscope that the patternedcholesteric liquid crystal layer had a periodically aligned surfacehaving a concentric circular shape (radial shape) as shown in FIG. 19 .In the liquid crystal alignment pattern of the patterned cholestericliquid crystal layer, regarding the single period over which the opticalaxis of the liquid crystal compound rotated by 180°, the single periodof a center portion was 181 µm, the single period of a portion at adistance of 5 mm from the center was 1.8 µm, the single period of aportion at a distance of 10 mm from the center was 1.0 µm. This way, thesingle period decreased toward the outer direction. In addition, theselective reflection center wavelengths of the patterned cholestericliquid crystal layer were 650 nm at the center portion, 700 nm at theposition at a distance of 5 mm from the center, and 750 nm at theposition at a distance of 10 mm from the center. That is, the pitch ofthe helical structure of the patterned cholesteric liquid crystal layerincreased toward the outside.

Comparative Example 2-2

A second cholesteric liquid crystal layer having a selective reflectioncenter wavelength of 650 nm and reflecting left circularly polarizedlight was formed using the same method as that of Comparative Example2-1, except that the chiral agent was changed to Ch-3 and the additionamount thereof was changed to 7.69 parts by mass. At this time, theirradiation dose of ultraviolet light was not changed in a plane as inComparative Example 2-1.

The second cholesteric layer was laminated on the optical elementaccording to Comparative Example 2-1 to prepare an optical element.

In a case where the cholesteric layer reflecting right circularlypolarized light and the second cholesteric layer reflecting leftcircularly polarized light were laminated, the reflecting layers werebonded to each other such that the directions in which the direction ofthe optical axis in the liquid crystal alignment pattern continuouslychanged were different from each other.

Chiral Agent Ch-3

Example 3

A composition A-4A for forming a second patterned cholesteric liquidcrystal layer was prepared using the same method as that of Example 2-1,except that the chiral agent was changed to Ch-4A and the additionamount thereof was changed to 7.40 parts by mass. This composition A-4Ais a liquid crystal composition forming a second patterned cholestericliquid crystal layer (cholesteric liquid crystalline phase) thatreflects left circularly polarized light.

Chiral Agent Ch-4A

In Example 2-1, the composition A-2A was changed to the compositionA-4A, the composition A-4A was applied to the alignment film P-1, andthe coating film was heated to 95° C. on a hot plate. Next, the coatingfilm was cooled to 25° C. and was irradiated with only ultraviolet light(i-ray) having a wavelength of 365 nm using a LED light source under anitrogen atmosphere. At this time, the coating film was irradiated whilechanging the irradiation dose of ultraviolet light in a plane.Specifically, the coating film was irradiated while changing theirradiation dose to 0 mJ/cm² (center portion), 45 mJ/cm² (the distanceof 5 mm from the center), and 90 mJ/cm² (the distance of 10 mm from thecenter) in a plane. Next, the coating film was heated to 95° C. on a hotplate, was cooled to 25° C., and was irradiated with mixed ultravioletlight having a wavelength of 350 nm or shorter using a high-pressuremercury lamp under a nitrogen atmosphere. As a result, the alignment ofthe liquid crystal compound was immobilized, and a second patternedcholesteric liquid crystal layer was formed. In addition, the selectivereflection center wavelengths of the second patterned cholesteric liquidcrystal layer were 650 nm at the center portion, 700 nm at the positionat a distance of 5 mm from the center, and 750 nm at the position at adistance of 10 mm from the center. That is, the pitch of the helicalstructure of the second patterned cholesteric liquid crystal layerincreased toward the outside. The second patterned cholesteric layer waslaminated on the optical element according to Example 2-1 to prepare anoptical element.

In a case where the patterned cholesteric layer reflecting rightcircularly polarized light and the second patterned cholesteric layerreflecting left circularly polarized light were laminated, thereflecting layers were bonded to each other such that the directions inwhich the direction of the optical axis in the liquid crystal alignmentpattern continuously changed were different from each other.

Example 2-4

A composition A-4B for forming a second patterned cholesteric liquidcrystal layer was prepared using the same method as that of Example 2-3,except that the chiral agent was changed to Ch-4B and the additionamount thereof was changed to 3.85 parts by mass. This composition A-4Bis a liquid crystal composition forming a patterned cholesteric liquidcrystal layer (cholesteric liquid crystalline phase) that reflects leftcircularly polarized light.

Chiral Agent Ch-4B

In Example 2-3, the composition A-4A was changed to the compositionA-4B, the composition A-4B was applied to the alignment film P-1, andthe coating film was heated to 95° C. on a hot plate. Next, the coatingfilm was cooled to 25° C. and was irradiated with only ultraviolet light(i-ray) having a wavelength of 365 nm using a LED light source under anitrogen atmosphere. At this time, the coating film was irradiated whilechanging the irradiation dose of ultraviolet light in a plane.Specifically, the coating film was irradiated while changing theirradiation dose to 0 mJ/cm² (center portion), 30 mJ/cm² (the distanceof 5 mm from the center), and 60 mJ/cm² (the distance of 10 mm from thecenter) in a plane. Next, the coating film was heated to 95° C. on a hotplate, was cooled to 25° C., and was irradiated with mixed ultravioletlight having a wavelength of 350 nm or shorter using a high-pressuremercury lamp under a nitrogen atmosphere. As a result, the alignment ofthe liquid crystal compound was immobilized. In addition, the selectivereflection center wavelengths of the second patterned cholesteric liquidcrystal layer were 650 nm at the center portion, 700 nm at the positionat a distance of 5 mm from the center, and 750 nm at the position at adistance of 10 mm from the center. That is, the pitch of the helicalstructure of the second patterned cholesteric liquid crystal layerincreased toward the outside. The second patterned cholesteric layer waslaminated on the optical element according to Example 2-2 to prepare anoptical element.

In a case where the patterned cholesteric layer reflecting rightcircularly polarized light and the second patterned cholesteric layerreflecting left circularly polarized light were laminated, thereflecting layers were bonded to each other such that the directions inwhich the direction of the optical axis in the liquid crystal alignmentpattern continuously changed were different from each other.

Preparation of Circular Polarization Plate

In order to perform “Measurement of Light Intensity” described below, acircular polarization plate was prepared as described below.

First, the support on which the undercoat layer was formed was preparedusing the same method as that of Example 2-1.

Formation of Alignment Film P-10

The following alignment film P-10-forming coating solution wascontinuously applied to the support on which the undercoat layer wasformed using a #2.4 wire bar. The support on which the coating film ofthe alignment film P-10-forming coating solution was formed was driedusing a hot plate at 80° C. for 5 minutes. As a result, an alignmentfilm P-10 was formed.

Alignment Film P-10-Forming Coating Solution Material forphoto-alignment Polymer A2 ...  4.35 parts by mass Low molecular weightcompound B2  ...   0.80 parts by mass Crosslinking agent C1  ...  2.20parts by mass Compound D1  ...  0.48 parts by mass Compound D2  ... 1.15 parts by mass Butyl acetate  ...  100.00 parts by mass

Synthesis of Polymer A2

100 parts by mass of 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 500parts by mass of methyl isobutyl ketone, and 10 parts by mass oftriethylamine were charged into a reaction vessel equipped with astirrer, a thermometer, a dripping funnel, and a reflux cooling pipe andwere mixed with each other at room temperature. Next, 100 parts by massof deionized water was dropped for 30 minutes using a dripping funnel,and a reaction was caused to occur at 80° C. for 6 hours while mixingthe components with each other under reflux. After completion of thereaction, the organic phase was extracted and was cleaned with 0.2 mass%ammonium nitrate aqueous solution until water used for cleaning wasneutral. Next, by distilling off the solvent and water under reducedpressure, epoxy-containing polyorganosiloxane was obtained as a viscoustransparent liquid.

In a case where the epoxy-containing polyorganosiloxane was analyzed bynuclear magnetic resonance (¹H-NMR), a peak having a theoreticalintensity based on an oxiranyl group was obtained in the vicinity ofchemical shift (δ)=3.2 ppm, and it was verified that a side reaction ofan epoxy group did not occur during the reaction. In theepoxy-containing polyorganosiloxane, the weight-average molecular weightMw was 2,200, and the epoxy equivalent was 186 g/mol.

Next, 10.1 parts by mass of the epoxy-containing polyorganosiloxaneobtained as described above, 0.5 parts by mass of an acrylicgroup-containing carboxylic acid (manufactured by Toagosei Co., Ltd.,ARONIX M-5300, ω-carboxypolycaprolactone monoacrylate (polymerizationdegree n ≈ 2)), 20 parts by mass of butyl acetate, 1.5 parts by mass ofa cinnamic acid derivative obtained using a method of Synthesis Example1 of JP2015-026050A, and 0.3 parts by mass of tetrabutylammonium bromidewere charged into a 100 mL three-neck flask, and were stirred at 90° C.for 12 hours. After completion of the reaction solution was diluted withthe same amount (mass) of butyl acetate as that of the reaction solutionand was cleaned with water three times.

An operation of concentrating this solution and diluting theconcentrated solution with butyl acetate was repeated twice. Finally, asolution including polyorganosiloxane (the following polymer A2) havinga photo-alignable group was obtained. In the polymer A2, theweight-average molecular weight Mw was 9,000. In addition, as a resultof ¹H-NMR, the content of a component having a cinnamate group in thepolymer A2 was 23.7 mass%.

Polymer A2

Low Molecular Weight Compound B2

The low molecular weight compound B2 shown in the following table(manufactured by Nissin Ion Equipment Co., Ltd., NOMCOAT TAB) was used.

Crosslinking Agent Cl

The crosslinking agent C1 (manufactured by Nagase ChemteX Corporation,DENACOL EX411) shown in the following table was used.

Compound D1

The following compound D1 (manufactured by Kawaken Fine Chemicals Co.,Ltd., ALUMINUM CHELATE A(W)) shown in the following table was used.

Compound D2

The compound D2 (manufactured by Toyo Science Corp., triphenylsilanol)shown in the following table was used.

Exposure of Alignment Film P-10

By irradiating the obtained alignment film P-10 with polarizedultraviolet light (20 mJ/cm², using an extra high pressure mercurylamp), the alignment film P-10 was exposed.

Preparation of Optically-Anisotropic Layer (λ/4 Plate)

An optically-anisotropic layer was formed by applying the compositionC-1 to the alignment film P-10. The applied coating film was heatedusing a hot plate at 110° C., the coating film was cooled to 60° C., andthe coating film was irradiated with ultraviolet light having awavelength of 365 nm at an irradiation dose of 500 mJ/cm² using ahigh-pressure mercury lamp in a nitrogen atmosphere. As a result, thealignment of the liquid crystal compound was immobilized, and anoptically-anisotropic layer was prepared.

In the obtained optically-anisotropic layer, Δn₆₅₀ × d (Re(650)) was162.5 nm.

Preparation of Circular Polarization Plate

A linear polarizing plate was bonded to the triacetyl cellulose filmside of the optically-anisotropic layer (λ/4 plate) through a pressuresensitive adhesive to obtain a circular polarization plate.

Measurement of Reflection Angle

In a case where light was incident into the prepared optical elementfrom the normal direction (the front; a direction with an angle of 0°with respect to the normal line), angles (reflection angles) ofreflected light of red light with respect to the incidence light weremeasured. It was assumed that light was incident from the surface wherethe patterned cholesteric liquid crystal layer was provided.

Specifically, each of laser beams having an output center wavelength ina red light range (650 nm) was caused to be vertically incident into theprepare optical element from a position at a distance of 100 cm in thenormal direction, and reflected light was captured using a screendisposed at a distance of 100 cm to calculate a reflection angle.

Laser light was caused to be vertically incident into the circularpolarization plate prepared as described above corresponding to thewavelength of the laser light to be converted into right circularlypolarized light, the right circularly polarized light was incident intothe prepared optical element, and the evaluation was performed.

Measurement of Light Intensity

Using a method shown in FIG. 21 , a relative light intensity wasmeasured.

In a case where light was incident into the prepared optical elementfrom the front (direction with an angle of 0° with respect to the normalline), a relative light intensity of reflected light with respect to theincidence light was measured.

Specifically, laser light L having an output center wavelength of 650 nmwas caused to be vertically incident from a light source 98 into theprepared optical element S. A light intensity of reflected light L,reflected at a reflection angle θ was measured using a photodetector 99.A ratio between the light intensity of the reflected light L_(r) and thelight intensity of the light L was obtained to obtain the value of therelative light intensity of the reflected light L_(r) relative to theincidence light (laser light L) (reflected light L_(r)/laser light L).As the reflection angle θ, the reflection angle measured in advance wasused.

In each of the liquid crystal alignment patterns of the patternedcholesteric liquid crystal layers of the prepared optical elementsaccording to Comparative Examples 2-1 and Examples 2-1 and 2-2, laserlight was caused to be vertically incident into a position at a distanceof 0.7 mm from the center of the concentric circle and a position at adistance of 10 mm from the center of the concentric circle, a relativelight intensity of the reflected light relative to the incidence lightwas measured, and the results thereof were compared to each other. InComparative Example 2-1, the reflection angle θ of the light incidentinto the position at a distance of 0.7 mm from the center of theconcentric circle was 3°, and the reflection angle θ of the lightincident into the position at a distance of 10 mm from the center of theconcentric circle was 41°. In Comparative Example 1, a relative lightintensity of the reflected light relative to the light incident into theposition at a distance of 10 mm from the center of the concentric circlewas significantly lower than that of the reflected light relative to thelight incident into the position at a distance of 0.7 mm from the centerof the concentric circle. In Examples 2-1 and 2-2, the reflection angleθ of the light incident into the position at a distance of 0.7 mm fromthe center of the concentric circle was 3°, and the reflection angle θof the light incident into the position at a distance of 10 mm from thecenter of the concentric circle was 41°. In Examples 2-1 and 2-2, in acase where a relative light intensity of the reflected light relative tothe light incident into the position at a distance of 10 mm from thecenter of the concentric circle was compared to that of the reflectedlight relative to the light incident into the position at a distance of0.7 mm from the center of the concentric circle, it was found that adecrease in relative light intensity was suppressed, and the reflectionangle dependence of the amount of light reflected in a plane was able tobe reduced as compared to Comparative Example 1.

The evaluation of Comparative Examples 2-2 and Examples 2-3 and 2-4 wasperformed using the same method as that of Comparative Example 2-1,except that laser light incident into the prepared optical element didnot pass through the circular polarization plate. In the evaluation ofComparative Examples 2-2 and Examples 2-3 and 2-4, in Examples 2-3 and2-4, the reflection angle dependence of the amount of light reflected ina plane was able to be reduced as compared to Comparative Example 2-2.In addition, in Examples 2-3 and 2-4, a large amount of light reflectedwas obtained for polarized light other than circularly polarized light.

As shown in the above results, in the optical element according to theembodiment of the present invention including a cholesteric liquidcrystal layer, in which the cholesteric liquid crystal layer has aliquid crystal alignment pattern in which a direction of an optical axisderived from a liquid crystal compound changes while continuouslyrotating in at least one in-plane direction, the cholesteric liquidcrystal layer has regions having different pitches of helical structuresin a plane, and the cholesteric liquid crystal layer has regions havingdifferent lengths of the single periods of the liquid crystal alignmentpatterns in a plane, the reflection angle dependence of the amount oflight reflected can be reduced. In particular, as in Examples 2-1 and2-2, in a case where, in regions having different lengths of singleperiods of liquid crystal alignment patterns, a permutation of thelengths of the single periods and a permutation of the lengths(selective reflection center wavelengths) of the pitches of the helicalstructures in the cholesteric liquid crystal layers are different fromeach other, a larger amount of light reflected can be obtained.

In addition, as in Examples 2-3 and 2-4, in a case where a plurality ofcholesteric liquid crystal layers having different twisted directions(directions of circularly polarized light to be reflected) of helicalstructures of the cholesteric liquid crystal layers are combined, alarger amount of light reflected can also be obtained for variousincident polarized light.

The present invention is suitably applicable to various uses where lightis reflected in an optical device, for example, a diffraction elementthat causes light to be incident into a light guide plate of AR glassesor emits light to the light guide plate.

EXPLANATION OF REFERENCES 10, 10 b optical element 12 reflection member14 first reflecting layer 20 support 24 alignment film 26, 26 b, 34patterned cholesteric liquid crystal layer 30 liquid crystal compound30A optical axis 60, 80 exposure device 62, 82, 98 laser 64, 84 lightsource 65 λ/2 plate 68, 86, 94 polarization beam splitter 70A, 70B, 90A,90B mirror 72A, 72B, 96 λ/4 plate 92 lens 99 photodetector 100 linearpolarizer 102 λ/4 plate 104 light screen 104 a pinhole 110 light guideelement 112 light guide plate 114 first diffraction element 116 seconddiffraction element 118 third diffraction element 120 dove prism 122linear polarizer 124 λ/4 plate M laser light MA, MB beam MP P polarizedlight MS S polarized light Po linearly polarized light P_(R) rightcircularly polarized light P_(L) left circularly polarized light αintersection angle Q absolute phase E equiphase surface S sample L lightL_(r) reflected light I₀ to I₃ light propagated in light guide plate P₁to P₄ position R₁ to R₄ light PT₁, PT₂ helical pitch

What is claimed is:
 1. An optical element comprising a plurality ofpatterned cholesteric liquid crystal layers that are obtained byimmobilizing a cholesteric liquid crystalline phase, wherein thepatterned cholesteric liquid crystal layers have different twisteddirections of helical structures, the patterned cholesteric liquidcrystal layers have a liquid crystal alignment pattern in which adirection of an optical axis derived from a liquid crystal compoundchanges while continuously rotating in at least one in-plane direction,the patterned cholesteric liquid crystal layers have regions havingdifferent pitches of helical structures in a plane, in a case where alength over which the direction of the optical axis derived from theliquid crystal compound rotates by 180° in a plane is set as a singleperiod, the patterned cholesteric liquid crystal layers have regionshaving different lengths of the single periods, the patternedcholesteric liquid crystal layers having different twisted directions ofthe helical structures have the same selective reflection centerwavelength, and in the patterned cholesteric liquid crystal layershaving different twisted directions of helical structures, directions inwhich the direction of the optical axis derived from the liquid crystalcompound continuously rotates in the liquid crystal alignment patternare different from each other.
 2. The optical element according to claim1, wherein in the patterned cholesteric liquid crystal layer, a pitch ofa helical structure is larger in a region where the length of the singleperiod is shorter and a reflection angle of reflected light is larger,and the pitch of the helical structure is smaller in a region where thelength of the single period is longer and the reflection angle of thereflected light is smaller.
 3. The optical element according to claim 1,wherein in the patterned cholesteric liquid crystal layer, the length ofthe single period in the liquid crystal alignment pattern graduallydecreases in the in-plane direction in which the direction of theoptical axis derived from the liquid crystal compound changes whilecontinuously rotating in the liquid crystal alignment pattern.
 4. Theoptical element according to claim 1, wherein the liquid crystalalignment pattern is a concentric circular pattern having a concentriccircular shape where the in-plane direction in which the direction ofthe optical axis derived from the liquid crystal compound changes whilecontinuously rotating moves from an inside toward an outside.
 5. Theoptical element according to claim 1, wherein the length of the singleperiod in the liquid crystal alignment pattern is 50 µm or less.